John Mearsheimer’s academic roots: a reference publication year spectroscopy of a political scientist’s oeuvre

John J. Mearsheimer is one of the most renowned theorists of International Relations and is often regarded as one of the primary representatives of the theoretical school of neorealism. To be able to understand and classify his positions, it is necessary to investigate his (theoretical) backgrounds and academic roots. The aim of this paper is, therefore, to analyze the roots of this political scientist with the help of the method Reference Publication Year Spectroscopy (RPYS)—a specific kind of cited reference analysis—using the program CitedReferenceExplorer (CRExplorer). In the statistical analyses, we compiled a list of the most cited works by Mearsheimer and conducted an analysis of temporal peaks in these works. The dataset used for the analyses was taken from the Web of Science database (WoS, Clarivate): 59 publications with 2061 non-distinct cited references. The list of the 16 most frequently cited references in the publication set shows various texts and authors that seem to be important for Mearsheimer’s academic work. Thematic focuses of cited publications as well as the type of publication indicate that the scientist’s respective works and texts are embedded in the corresponding publication periods. The analysis of the peaks in the referenced publication years illustrates the following: On the one hand, the publication years in which Mearsheimer derived his fundamental theory of International Relations can be inferred. On the other hand, later years show his subsequent thematic focuses and his preoccupation with current events and conflicts.


Introduction
In the wake of Russia's annexation of the Ukrainian peninsula of Crimea in 2014, U.S. political scientist John Joseph Mearsheimer published a text in the policy journal Foreign Affairs in the fall of 2014 entitled Why the Ukraine crisis is the West's fault: The liberal delusions that provoked Putin. In his text, he argues that the Western powers provoked Putin's aggression by moving into Russia's backyard as a result of the eastward expansion of the EU and NATO, and threatening Russia's core strategic interests (Mearsheimer, 2014). While the text attracted attention and caused heated debate in the political science community at the time, it was not until almost a decade later that the conflict, and to a lesser extent, Mearsheimer's arguments, attracted significant public interest at the global level. Eight years after the appearance of the text, Putin's Russia is waging a war of aggression against all of Ukraine. In various interviews, lectures and guest articles, Mearsheimer is once again opposing what he sees as a false view of the Western mainstream which portrays Putin as an irrational, aloof aggressor hell-bent on creating a greater Russia modeled on the Soviet Union. According to Mearsheimer's analysis, the Russian aggressions are a response to Western expansion (see https:// www. econo mist. com/ by-invit ation/ 2022/ 03/ 11/ john-mears heimer-on-why-the-west-is-princ ipally-respo nsible-for-the-ukrai nian-crisis).
To be able to understand and classify positions such as these, not only information and discourses on the conflict and the thematic field are necessary, but also the (theoretical) backgrounds and academic roots of the person taking a position . Bibliometric methods such as cited reference analysis can play an important role here. The aim of this paper is, therefore, to analyze the academic roots of the political scientist Mearsheimer. Mearsheimer is one of the most renowned theorists of International Relations and is often regarded as one of the primary representatives of the theoretical school of neorealism. His involvement in current discussions and the attention generated by it highlight his existing relevance in the academic field of international politics. With the help of a Reference Publication Year Spectroscopy (RPYS), a specific kind of cited reference analysis , a list of the most cited works by Mearsheimer will be compiled, and an analysis of temporal peaks in his cited works will be conducted to explore his academic roots. RPYS focusses on publications only and is not able to cover discussions beyond publications. Another limitation of the method concerns the consideration of document types in the analysis: only journal papers, but not books can be used as starting point for the RPYS.
To create a context for the classification of the findings, we will begin by presenting Mearsheimer's life, work, and his most important theories and positions.

Mearsheimer's life, work and theory
Background information on the academic career and substantive positions and theories of Mearsheimer is indispensable for the examination of his academic roots, works cited and their interpretative classification.
Mearsheimer was born on December 14, 1947, in Brooklyn, New York City. At the age of 17, he joined the U.S. Army, which allowed him to attend the United States Military Academy after one year (Booth et al., 2006) Throughout his academic career, Mearsheimer engaged with a variety of subjects surrounding International Relations and military theory. The school of thought Mearsheimer can be attributed to within International Relations is Neorealism, or more specifically, offensive Neorealism. Neorealism adopts the assumptions of Hans Morgenthau's classical realism, according to which the primary actors in international politics are states in an international system of anarchy in which cooperation occurs only extremely rarely. These states, according to Neorealism, compete for security, which is expressed mainly through military means. Some variations exist within this school (of theory). In defensive neorealism, political scientist Kenneth Waltz, the founder of neorealism, posits that states in the international system strive for a balance of power which, if not established through a bipolar order, comes about through alliances. This balance of power is supposed to secure peace. In The Tragedy of Great Power Politics, Mearsheimer contradicts this thesis by explaining that states are not satisfied with their security within a balance of power system; they try to expand their own power to achieve a hegemony status (Mearsheimer, 2001).
Another topic of International Relations that Mearsheimer is engaged in is the Israel-Palestine-conflict and the relation between the U.S. and Israel. In many publications such as The Israel Lobby and U.S. Foreign Policy (Mearsheimer & Walt, 2006), Mearsheimer and his colleague Harvard Professor of International Relations Stephen M. Walt describe the influence of a "loose coalition of individuals and organizations actively working to steer U.S. foreign policy in a pro-Israel direction" (Mearsheimer & Walt, 2006: p. 40). According to Mearsheimer and Walt (2006), the strategies promoted by this coalition are not in the U.S. national interest, and even not in the Israeli interest. The discussions around these publications including the book The Israel Lobby and U.S. Foreign Policy (Mearsheimer & Walt, 2007) following the paper caused much debate in the U.S. media, where, among other things, the authors were accused of anti-Semitism.
Mearsheimer's more recent works go beyond the scope of International Relations and are concerned with broader questions about political systems (while still relating to international conflicts). In various works like Bound to Fail: The Rise and Fall of the Liberal International Order (Mearsheimer, 2019), Mearsheimer describes what he sees as the false idea and objective of spreading liberal hegemony: the global efforts to transform more and more nations into democracies, steer them towards liberal market economies, and overall strengthen liberal and democratic cultures. Mearsheimer deemed this idea of liberal hegemony as doomed to fail: on the one hand, nationalist opposition to liberal expansion is being provoked internationally, especially by Russia and China. On the other hand, internationalist liberalism causes conflict with nationalist tendencies within liberal democracies. He sees Brexit and Trump as clear examples of this (Mearsheimer, 2019). This view of the expansion of liberal democracy partly forms the basis for statements mentioned in the introduction regarding the Russian war in Ukraine.

Methods and dataset
To analyze Mearsheimer's academic roots, this study uses a bibliometric method: the cited reference analysis. This method analyzes the impact of scientific publications in another way as the usual times cited analysis. The times cited analysis counts the number of citations the publications in a set receive after their publication in the following years. Cited reference analysis instead has a backward view on citation impact: the analysis starts by selecting all publications on a particular topic, field of research, or person, and then identifies the most important and influential references that are cited from this selection (Bornmann & Marx, 2013). In this way, it is possible to examine the historical roots and theoretical background of a topic, field of research, or person. The RPYS is a specific application of cited reference analysis that visualizes the frequency with which referenced publication years are cited in publications of a given dataset (of a topic, field of research, or person) .
A program that facilitates the analysis of a publication set as well as the visualization of the results is the CitedReferenceExplorer (CRExplorer), which was used in this study. The dataset used for the RPYS here was taken from the Web of Science database (WoS, Clarivate). 59 publications with 2170 non-distinct cited references were found in the WoS under the name John Mearsheimer (WoS author profile, date of search: September 2022). This dataset was edited in the CRExplorer then. The CRExplorer offers the option of disambiguating cited references. In this process, different variations of the same cited reference are recognized by adjustable similarity measures and can be merged into one reference. Using this method for revising the publication set, 2061 different cited references remain with which the cited reference analysis was performed. Whereas the range of citing publication years in the publication set is from 1981 to 2021, the range of cited publication years is from 1883 to 2020.
Our set with Mearsheimer's publications only contains papers published in journals that are covered by the WoS. Mearsheimer's monographs as well as guest articles in newspapers such as the article in the Economist cited in Sect. "Introduction" are, therefore, not included as (citing) sources in the RPYS. However, a comparison of the papers in the publication set of this study and the publication list on Mearsheimer's website shows that the publication set, without being completely exhaustive, provides a good representation of his research. We assume, therefore, that the part of his entire works in the publication set of this study may allow 'valid' conclusions to be drawn about his theoretical background. For various books by Mearsheimer, for example, such as The Great Delusion: Liberal Dreams and International Realities (Mearsheimer, 2018) or The Israel Lobby and U.S. Foreign Policy (Mearsheimer & Walt, 2007), the publication set also includes papers whose thematic focus corresponds to the books and which contain his core theses.
Using Mearsheimer's publications (from the WoS), the CRExplorer can generate results indicating Mearsheimer's academic roots. Two figures have been produced with the program. One figure illustrates the number of cited references in each (referenced) publication year, and shows the deviation of this number (in one year) from the median number over a five-year period (in adjacent years). Another figure identifies important peaks based on the interquartile range of the median deviations (with positive values) (Tukey's fences, see Tukey, 1977).
In addition, the CRExplorer has been used to generate a list of all cited references, which have been sorted by the number of times a reference has been cited. We focus in the following on 16 publications that have been referenced at least four times.

Results
The findings of the cited reference analysis will now be described to reveal John Mearsheimer's academic roots. The list of the most frequently referenced sources is followed by an analysis of the referenced publication years that are characterized by peaks.

Analysis of the most referenced sources in Mearsheimer's publication set
A book or paper that is often cited as a source by a scientist across different publications can be very useful for extrapolating the academic roots. Fundamental theoretical works to which Mearsheimer refers several times, or works and scholars with whom he is in continuous discourse, significantly influence and shape his own ideas and theories. Table 1 shows the 16 most frequently cited references in Mearsheimer's oeuvre. The number of occurrences of the references are relatively low which results from the fact that the total number of cited references is relatively low in the dataset of this study and Mearsheimer obviously cites rather diversely than focused. The results in Table 1 reveal different trends. Formally, it can be observed that the most frequently cited references consist of eight book sources and eight papers from academic journals. The only non-academic source the list entails is the field manual book published by the U.S Department of the Army, which is cited four times. Furthermore, the results in the table indicate that the regional density of the publications is striking. Only one work, The Rise and Fall of British Naval Mastery (1976) by Paul M. Kennedy, was published in the UK.
All the other texts are not only by U.S. scholars and universities, but even all from a relatively small geographical area in the north-west of the USA. It is hardly surprising that the Northwestern states, which are home to the Ivy League universities and the political center of the country with the capital Washington, D.C., are an agglomeration for science in general and political science in particular. Moreover, Mearsheimer was born here and completed most of his professional and academic career in this region. A similar consistency can be seen with regard to the gender of the authors of the publications, which is without exception male, with the small caveat of the U.S. Army field manual not having a singular main author stated. This can partly be explained by the fact that women are still significantly underrepresented in science, especially in the twentieth century, when most of the works on the list were published. However, political science as a social science is at least more likely than other fields to be associated with a greater number of female scholars. With regard to the year of publication, there is a strong focus around the 1980s, which coincides with the beginning of Mearsheimer's academic training.
In terms of content, the list includes some well-known publication titles and authors. Kenneth Waltz's Theory of International Politics (1979), which, together with one of Mearsheimer's own works Conventional Deterrence (Mearsheimer, 1983), ranks first on the list with seven references. This is not only a handbook of the neorealist International Relations theory, Waltz is also one of Mearsheimer's peers with whom he conducted the most academic discourse. Mearsheimer's most popular work, The Tragedy of Great Power Politics (2001) can, in many respects, be interpreted as a response to and further development of the Theory of International Politics (Waltz, 1979). The importance of Waltz for Mearsheimer is underlined by the fact that an interview with him is also part of the list above.
Below that, with six individual references, beside Mearsheimer's article Why the Soviets Can 't Win Quickly in Central Europe (1982), Barry Posen's Sources of Military Doctrine (1984) can be found. Sources of Military Doctrine is a foundational book dealing with the intersection of military theory and International Relations. This subject area is and was of great importance to Mearsheimer, especially at the beginning of his academic career. This can be seen, for example, in his second book Liddell Hart and the Weight of History (1988), which contains a strong reference to military theory. Other works on the list of most frequently cited references also reflect the focus on this topic, like The Rise and Fall of British Naval Mastery (Kennedy, 1976), Surprise Attack: Lessons for Defense Planning (Betts, 1982), Mearsheimer's own works Why the Soviets Can't Win Quickly in Central Europe (1982) and Maneuver, Mobile Defense, and the NATO Central Front (1981), as well as of course the U.S. Army field manual (1976). 1 3 Another publication on the list is Francis Fukuyama's The End of History? (1989), the precursor to the book of the same name on the world order after the end of the Cold War. After Hegemony (1984) by Robert Keohane is regarded as one of the main works of liberal institutionalism in International Relations and is diametrically opposed to Mearsheimer's school of theory. It is also worth mentioning that Barry R. Posen and Stephen van Evera are the only persons besides Mearsheimer himself to appear several times in the 16 publications. While Posen is mostly seen as a classical realist, van Evera, like Waltz is a follower of the defensive variant of neorealism and has a close theoretical relationship to Mearsheimer.

Analysis of peaks in reference publication years
The temporal component of a scientist's academic roots can be illustrated well by RPYS. The spectrogram shows how many referenced publications were published in which years and how great the deviation from the temporal development is. In this section of the paper, the years with the greatest deviation are identified and possible causes of the most important peaks are interpreted. Figure 1 shows the spectrogram of the cited reference analysis. It indicates the number of cited references in each reference publication year. In order to receive hints for years with relatively high numbers of referenced publications-these are probably years with Mearsheimer's historical roots-median deviations are also visualized. Since the median deviations in Fig. 1 point to many years with relatively high numbers, we additionally used Tukey's fences (Tukey, 1977) to get hints on the most important peaks.  Table 2 lists the referenced publication years from Fig. 2 with reference publication years that are 'outliers' (lower line) or 'far out ' (upper line).
The year with the greatest deviation, 2018, inevitably contains cited references from very late works by Mearsheimer. The thematic focus is on the global development towards nationalism as a challenge to liberal systems. Important publications by Mearsheimer from after this time period (which cite the publications from the year in question) include, for

Discussion and conclusions
After an overview of Mearsheimer's life and work, this study analyzed the results of a cited reference analysis based on a dataset of his publications in the WoS. The list of the most influential sources on the work of this political scientist represents a selection of key texts on International Relations and provides an insight into his fundamental academic roots. The list of the 16 most frequently cited references in the publication set shows various texts and authors that seem to be important for Mearsheimer's academic work. The most important sources originated in the Northwest of the U.S. during the 1980s. In terms of content, however, there is a diversity of opinion in Mearsheimer's academic oevre. This is illustrated by the publications by renowned political scientists supporting different opinions that occur among the most frequently cited references by Mearsheimer. Despite the relatively small dataset, we were able to analyze and classify the peaks in the RPYS on Mearsheimer's academic work. The analysis of the peaks in the referenced publication years illustrates two things. On the one hand, the publication years in which Mearsheimer derived his fundamental theory of International Relations can be inferred. On the other hand, later years show his subsequent thematic focuses and his preoccupation with current events and conflicts.
The RPYS allows statements to be made about the roots of Mearsheimer's theoretical work and the scientific communities to which he belongs. Despite a rather small publication set (used in this study), this study can contribute to a deeper understanding of Mearsheimer's theoretical background and academic roots. Positions such as those described in Sect. "Introduction" regarding the Ukraine conflict, for example, can be linked to Waltz's theories on the balance of power, according to which NATO expansion disturbs this balance. Waltz's influence on Mearsheimer's work, as shown above, might, therefore, at least partially explain Mearsheimer's blaming of the West. Even if Mearsheimer does not share the balance of power thesis in his own theory, and of course no clear line can be drawn from Waltz's theories to Mearsheimer's statements today, the roots of Mearsheimer's publications analyzed in this study nevertheless provide clues to positions and help explain them.
We already mentioned the small dataset as a possible limitation of the study. We would like to mention two other limitations (to make also clear which conclusions cannot be drawn from our results). (1) The initial dataset does not include Mearsheimer's books, which make up an important part of his work. Other results may appear with a dataset including the books. (2) In his dealing with international politics, Mearsheimer cited theoretical and empirical research as well as articles about current events. Some of these sources were cited by him to support his statements and theories, while others to argue against them. Because of the diversity in types of used texts and types of engagement, it is a challenge to interpret cited opinions, facts, theories etc. as possible roots of Mearsheimer (in this study).