Complex sentence: It was not common for a Japanese woman to study abroad at that time in Japan, even though the democratic days came after WWII, however, she decided to study the cause of the defeated war at the university in the USA.
Split into simpler sentences: It was not common for a Japanese woman to study abroad at that time in Japan, even though the democratic days came after WWII. She wanted to study the cause of the defeated war at the university in the USA.