According to Jun-ichi Igusa, Chow was able to communicate with European mathematicians during the first few years of his stay in China as a Professor at the Central University in Nanking, but then the situation became worse:
In the later years of our meetings, Professorand Mrs. Chow often mentioned the time when they were in China. After their marriage in Hamburg in July of 1936, they left Nazi Germany for China, and Chow started teaching at the Central University in Nanjing in September of that year. However, only one year later they found that China was no better than Germany. Imperial Japan enlarged a small fight on July 7, 1937, at the Marco Polo Bridge near Beijing to a systematic invasion of China. On August 13 a skirmish occurred in Shanghai, and on December 13 the “Rape of Nanjing” started. Fortunately they escaped Nanjing in September of that year to Chow’s birthplace, Shanghai. Shanghai being an international city, they felt safer there. They told us, however, that Shanghai at that time was quite similar to the Shanghai described in S. Spielberg’s movie, Empire of the Sun. In the first two to three years in China, Chow was still able to communicate with mathematicians in Europe, especially with van der Waerden. However, during the remaining eight years before he came to the United States the situation became so bad that he was unable to continue his mathematics. He told us more than once that it was Professor Chern who encouraged and helped him to come back to mathematics. Chow came to the Institute for Advanced Study in Princeton in March of 1947 and to Hopkins in the fall of 1948. He went on to say that without Chern’s friendship that might not have taken place.
But miraculously, Chow managed to return to his work after the war and: