While there are some problems with this question, the answer for it is clearly meant to be France. France was Vietnam’s colonial ruler and France was pushed out of Vietnam in 1954.
France had been dominating Vietnam since the mid-1800s. They had come to directly colonize the region and had continued to hold it until World War II. In WWII, the French lost to Germany and Vietnam was taken by Japan. After the war, Japan left and the French came back to recolonize. The Vietminh had been fighting against the Japanese and they now turned to armed conflict with France. In 1954, they won the war and France left.
It is not completely accurate to say that Vietnam then became independent. In fact, there was no single country of Vietnam until 1975. In 1954, Vietnam was divided into North Vietnam and South Vietnam. The people who had been the Vietminh ruled the North while a government backed by the United States ruled the South. Thus, it is a little bit misleading to say that “Vietnam” became independent as it was not a single country from 1954 to 1975.