What are the main causes of vietnam war and korean war?

After WWII and the decolonization period, both Vietnam and Korea were split up. The Northern section of both Korea and Vietnam were ruled by communist regimes. The Southern sections were Democratic/Republic governments.  The Vietnam rulers wanted to unit North and South Vietnam together, but under their own government, and the same with the two Koreas. After Russia builds their first Atomic bomb, though well after America's, Russia gives North Korea a go to attack South Korea. The UN immediately sends a makeshift army from multiple countries to support South Korea, and they battle back and forth until 1953, when the borders are the same as today's. This was about the exact same story with the Vietnam war, except Southern Vietnam immediately collapsed when President Richard Nixon pulled US troops out of Vietnam. These 2 wars were a series of conflicts between communist and non-communist regimes with Russia and US support known as the Cold War.

(d) rivers.

explanation:

civilizations developed around rivers because their waters provided places to hunt and fish. also, as the rivers flooded, the lands around them became fertile. this allowed them to support farming. this is especially true of the nile river, which flooded the same time each year.