Why do countries go to war? While economic, military, and geopolitical factors are often part of the answer, researchers have also pointed to exclusionary nationalism—the belief that one's own nation is superior to others. One observable trace of such sentiment is language: as exclusionary attitudes intensify, people tend to favor words from their own language over foreign ones, and even reject the "enemy's" words outright. History offers many examples, from the renaming of German-derived words in Britain during the First World War to recent restrictions on Russian-language print media in Ukraine. This pattern suggests that tracking the acceptance or rejection of foreign loanwords could serve as a window into exclusionary nationalism across countries and eras.
Prewar Japan offers an especially advantageous case for testing this idea, because the Japanese writing system makes it easy to tell foreign loanwords apart from native words. Japanese is written with three sets of characters: foreign-language words are usually transcribed in katakana, whereas traditional Japanese words use hiragana and kanji. For a foreign place name, writers could therefore choose either a katakana loanword or a kanji-based transliteration known as ateji. This built-in choice gives researchers a clear linguistic signal with which to observe shifting attitudes toward both allies and enemies before and after Japan entered the war in December 1941. The years leading up to the war were marked by several political events associated with rising nationalist sentiment in Japan. These included coup attempts by members of the Japanese military in 1932 and 1936, Japan's withdrawal from the League of Nations in 1933, the enactment of the National Mobilization Law in 1938, and the signing of the Tripartite Pact with Germany and Italy in 1940.
Given that exclusionary nationalism can either contribute to war or emerge in response to it, Associate Professor Tomoko Matsumoto from the Institute of Arts and Sciences at Tokyo University of Science (TUS), Japan, Visiting Associate Professor Yutaka Shimada of TUS and Saitama University, Japan, and former student Hiroyuki Hirate and Professor Tohru Ikeguchi, both from TUS, wondered whether shifts in nationalism could be traced through changes in language use.
They developed a statistical approach to track changes associated with exclusionary nationalism in newspapers and examine how these changes evolved before and after Japan entered the war in 1941.
Their findings, published in the journal PLOS One on July 8, 2026, suggest that changes in how foreign place names were written may reveal shifting attitudes toward foreign countries.
"This method makes it possible to quantitatively grasp the time-series changes in nationalism and perceptions of foreign countries from linguistic data, such as newspapers and social media, even in eras and regions where public opinion polls do not exist. Therefore, it is expected to be applicable to the early detection of international conflicts and social divisions in modern society," says the project team member, Prof. Matsumoto.
To track the emergence of exclusionary nationalism, the researchers analyzed how foreign place names were written in 300,110 newspaper articles published by 54 Japanese newspapers between 1912 and 1943. The Japanese language commonly uses katakana to phonetically represent foreign words, but foreign locations can also be written using kanji-based transliterations known as ateji. The researchers hypothesized that shifting away from foreign-sounding katakana and toward ateji could reflect growing exclusionary attitudes toward foreign countries.
Using a statistical method called singular spectrum transformation, the team tracked month-by-month changes in the use of ateji and katakana for foreign place names, focusing on the United States and the United Kingdom, which later became Japan's enemies, and Germany and Italy, which became allies.
The findings revealed that exclusionary nationalism in Japan did not steadily rise before the Pacific War but fluctuated over time. The researchers identified notable turning points in 1924, 1927, 1936, and 1938 that coincided with key political events. The use of katakana increased after 1924, coinciding with the appointment of the Foreign Minister, Kijūrō Shidehara, who promoted international cooperation. However, this trend slowed after his resignation in 1927 and shifted further following the February 26 coup attempt in 1936, a period associated with growing militarization.
Notably, katakana remained more common for German and Italian place names, highlighting differences in how Japan viewed future allies and enemies long before the war began.
In a world increasingly shaped by geopolitical tensions, understanding the forces that drive conflict is more important than ever. The researchers suggest that their method could help detect early signs of international conflict and social division by analyzing patterns in language use.
"This study deepens our understanding of the role of exclusionary nationalism in conflicts, highlighting its nuanced nature in shaping friend–enemy distinctions during wartime," notes the researchers.
Reference
Title of original paper: Identifying surge of exclusionary nationalism: A case study of prewar Japan
Journal: PLOS One
DOI: https://doi.org/10.1371/journal.pone.0349895
About The Tokyo University of Science
Tokyo University of Science (TUS) is a well-known and respected university, and the largest science-specialized private research university in Japan, with four campuses in central Tokyo and its suburbs and in Hokkaido. Established in 1881, the university has continually contributed to Japan's development in science through inculcating the love for science in researchers, technicians, and educators.
With a mission of "Creating science and technology for the harmonious development of nature, human beings, and society," TUS has undertaken a wide range of research from basic to applied science. TUS has embraced a multidisciplinary approach to research and undertaken intensive study in some of today's most vital fields. TUS is a meritocracy where the best in science is recognized and nurtured. It is the only private university in Japan that has produced a Nobel Prize winner and the only private university in Asia to produce Nobel Prize winners within the natural sciences field.
Website: https://www.tus.ac.jp/en/mediarelations/
About Associate Professor Tomoko Matsumoto from Tokyo University of Science
Dr. Tomoko Matsumoto is an Associate Professor at Tokyo University of Science, Japan. She received her Ph.D. in Politics from The University of Tokyo, Japan, in 2016. Her research focuses on quantitative political science, including public opinion, elections, redistribution, and elite mobility. She has published more than 10 papers and delivered over 70 presentations at academic conferences and workshops. She previously served as a Designated Lecturer at Nagoya University and as a Visiting Research Professor at New York University. In 2024, she received the Tokyo University of Science Outstanding Researcher Encouragement Award for her research achievements.
About Associate Professor Yutaka Shimada from Saitama University
Dr. Yutaka Shimada is an Associate Professor at Saitama University, Japan, and also a Guest Associate Professor at Tokyo University of Science (TUS), Japan. He received his D. E. degree from Saitama University in 2012. Prior to his current faculty role, he served as a postdoctoral researcher for the FIRST Aihara Innovative Mathematical Modelling Project at The University of Tokyo, Japan, and as an Assistant Professor at TUS. His research focuses mainly on network science and nonlinear time series analysis.
About Professor Tohru Ikeguchi from Tokyo University of Science
Dr. Tohru Ikeguchi is a Professor at the Department of Information and Computer Technology at the Tokyo University of Science (TUS), Japan. He received his B.E., M.E., and D.E. degrees from TUS. After working for nearly a decade as a full-time Professor at Saitama University, Japan, he served in TUS's Department of Management Science from 2014 to 2016 before joining his current department. His research interests include nonlinear time series analysis, computational neuroscience, application of chaotic dynamics to solving combinatorial optimization problems, and complex network theory. He has published over 230 papers and proceedings and refereed over 140 papers.
Funding information
Japan Society for the Promotion of Science KAKENHI under grant numbers JP22K18419, JP21H03514, JP23K21706, JP21H04391, JP20H00596, and JP18K12701.
