Agricultural communities settled where they did because there was a water source near by for growing crops. It is very hard to grow plants or raise animals without a water source. People also settled near water sources so they could travel on ships and trade with other communities along the same water source. The people in the community also needed water to stay hydrated and to wash dirty clothes or to bathe.
Khmer Rouge is associated with Cambodia.
To get them more things in life
Because LBJ, under the Tolkien Resolution, was given basically infinite power to protect U.S interests in Vietnam. Thus, President Johnson continued to "escalate", or build up American forces, weapons, and intervention in Vietnam. Now, somewhat opposite of this would be "Vietnamization" under Nixon, which was the gradual withdrawal of American troops but a continuation of supplies in order to aid South Vietnam from the Vietcong.