On the end days of April, the outside of South was research by North Vietnamese Army. So American thought they can't stay in Sai Gon anymore time, they needed to leave. They left Sai Gon by helicopter or fixed-wing aircraft. And on morning April 30,1975 , it was 7pm , The North Vietnamese Army came to the Independence Place and the flag of Communism was append on the top building. It was quickly renamed Ho Chi Minh City in honor of their revolutionary leader Ho Chi Minh, who had died several years before. And it ended the Vietnam war.