His scholarship is divided into three fields.
February Revolution and Russian Revolution The first is on the Russian Revolution. He published
The February Revolution: Petrograd 1917 in 1980. Hasegawa later returned to the February Revolution. He revised and updated the original book, re-evaluating the role of the liberals as active participants in the revolution. The revised and expanded edition,
The February Revolution, Petrograd, 1917: The End of the Tsarist Regime and the Birth of Dual Power, was published in 2017. He has embarked on new research on a social history of the Russian Revolution, focusing on crime, police, and mob justice. He published,
Crime and Punishment in the Russian Revolution: Mob Justice and Police in Petrograd, in 2017. His life-long interest in the February Revolution has culminated in the publication:
The Last Tsar: the Abdication of Nicholas II and the Fall of the Romanovs (Basic Books: 2024).
Russo-Japanese relations Recent
Russo-Japanese relations are the second area on which Hasegawa has done research. His research resulted in the publication
The Northern Territories Dispute and Russo-Japanese Relations in 1998. In these volumes Hasegawa examines the tortuous relations between Russia and Japan over the territorial dispute over what the Japanese call the "Northern Territories" and what the Russian call "the southern Kuril islands."
End of war with Japan The third area of research Hasegawa has conducted is an international history involving the Soviet Union, the United States, and Japan in ending the allied war with Japan. As the United States dropped its first atomic bombs on Hiroshima on 6 August 1945, 1.6 million
Soviet troops launched a surprise attack on the Japanese forces that occupied
Eastern Asia on the 9 August 1945. Hasegawa published a book,
Racing the Enemy: Stalin, Truman, and the Surrender of Japan (2005), challenging the widely accepted orthodox view that the atomic bombings on Hiroshima and Nagasaki were the most decisive factor in Japan's decision to surrender ending the
war against Japan. Hasegawa puts forward the view that the Soviet entry into the war, by breaking of the
Neutrality Pact, played a more important role than the atomic bombs in Japan's decision to surrender. That view is in contrast to earlier critics of the bombing, such as
Gar Alperovitz, who argued that US President
Harry S. Truman's underlying objective was showcasing the might of the
US military as a deterrent to the ambitions of the Soviet leader
Joseph Stalin. According to the Australian historian
Geoffrey Jukes, "[Hasegawa] demonstrates conclusively that it was the Soviet declaration of war, not the atomic bombs, that forced the Japanese to surrender unconditionally." His view has received criticism. The most balanced and spirited discussion of this book is given in an H-Diplo roundtable discussion with Gar Alperovitz, Michael Gordin, David Holloway, Richard Frank, and Baron Bernstein. == Publications ==