Martin Luther King Jr. (1929-1968) was the leader of the civil rights movement and an American baptist, he spent his life fighting peacefully for civil rights, specially on those concerning African American people.
During his speech Beyond Vietnam, which he gave on April 4, 1967 at Riverside Church King gives seven reasons for why he was interested in the Vietnam war.
The first reason King states is that few years back poor people in America had found hope through the poverty program that the government had designed, but when the war in Vietnam started the program was broken down. He stated that the government was investing more money and resources on Vietnam than on his own poor citizens that needed those economic resources.
The reason is logical because poor people were finally seeing some way out of their situation with the help of the government, and then they saw the resources went to another country.