Complex sentence: The National Mobilization Committee to End the War in Vietnam was a relatively short-lived coalition of antiwar activists formed in 1967 to organize large demonstrations in opposition to the war in Vietnam.
Split into simpler sentences: The National Mobilization Committee to End the War in Vietnam was a relatively short-lived coalition of antiwar activists formed in 1967 to organize large demonstrations in opposition to the Vietnam war. That committee was the National Mobilization Committee to End the War in Vietnam.