East Asia in the 21st Century and Historical Problems: Political History for Thinking and Dialogue (Tanaka Hitoshi ed., kyoto: Horitsu-Bunkasha, 2017) is a result of the long-term collaborative research by political scientists and historians of Japan, China, Taiwan, Korea, and Singapore. Based on what I learned from this book and from my experience of participating in a collaborative historical research project, I present my opinion about Sino-Japanese historical problems in the following order: emergence and expression of historical problems; how to solve historical problems academically; international collaborative research as the best route to the solution of historical problems.