Manifest destiny- the settlers believed God had given them the duty to settle and 'civilise' American land.
Freeing the slaves, the government, uncompromising diffrences , power of government over the states, economic changes , union was rapidly changing, and that's just a few I remember !!
It occurred chiefly due to the economic interventionism of the Japanese government and partly due to the aid and assistance of the U.S. aid to Asia. After World War II, the U.S. established a significant presence in Japan to slow the expansion of Soviet influence in the Pacific.