Hello!
The correct answer is economic chaos after war.
The Kamakura Shogunate (bafuku) was a Japanese feudal government from 1185 to 1333.
During 1274 and 1281 the Mongols tried to invade Japan, but they were repelled succesfully by the Japanese army. However, the military costs weakened the economy contributing to the decline of the Kamakura Bakufu.
Hope this helps