The establishment of Fidel Castro as the Prime Minister for military and political power was a development that led to the situation described. With Castro in high position, he set up a Communist government that the Soviet Union recognized and opted to aid, hence the U.S.'s opposition and attempted invasion.
Explanation:
The United States was democratic and the Soviets were Communist during the Cold War, so when the U.S. saw Cuba being led by a pro-communist, they saw a potential threat and took the initiative.
Child labor was virtually eliminated when, for the first time in history, the productivity of parents in free labor markets rose to the point that it was no longer economically necessary for children to work in order to survive.
Manchuria rich in natural resources and sparsely populated had obvious advantages for a densely populated and resource-poor Japan. Amongst Manchuria's resources coveted by Japan were iron, coking coal, soybeans, salt and above all land, all severely lacking within the Japanese empire in 1930.
