Which of the following best explains the change in US military combat deaths in Vietnam between 1964 and 1968 as depicted in the graph?

The entry of the United States into World War II caused vast changes in virtually every aspect of American life. Millions of men and women entered military service and saw parts of the world they would likely never have seen otherwise. The labor demands of war industries caused millions more Americans to move--largely to the Atlantic, Pacific, and Gulf coasts where most defense plants located. When World War II ended, the United States was in better economic condition than any other country in the world. Even the 300,000 combat deaths suffered by Americans paled in comparison to any other major belligerent.

Building on the economic base left after the war, American society became more affluent in the postwar years than most Americans could have imagined in their wildest dreams before or during the war. Public policy, like the so-called GI Bill of Rights passed in 1944, provided money for veterans to attend college, to purchase homes, and to buy farms. The overall impact of such public policies was almost incalculable, but it certainly aided returning veterans to better themselves and to begin forming families and having children in unprecedented numbers.

Not all Americans participated equally in these expanding life opportunities and in the growing economic prosperity. The image and reality of overall economic prosperity--and the upward mobility it provided for many white Americans--was not lost on those who had largely been excluded from the full meaning of the American Dream, both before and after the war. As a consequence, African Americans, Hispanic Americans, and American women became more aggressive in trying to win their full freedoms and civil rights as guaranteed by the Declaration of Independence and U.S. Constitution during the postwar era.

The postwar world also presented Americans with a number of problems and issues. Flushed with their success against Germany and Japan in 1945, most Americans initially viewed their place in the postwar world with optimism and confidence. But within two years of the end of the war, new challenges and perceived threats had arisen to erode that confidence. By 1948, a new form of international tension had emerged--Cold War--between the United States and its allies and the Soviet Union and its allies. In the next 20 years, the Cold War spawned many tensions between the two superpowers abroad and fears of Communist subversion gripped domestic politics at home.

In the twenty years following 1945, there was a broad political consensus concerning the Cold War and anti-Communism. Usually there was bipartisan support for most US foreign policy initiatives. After the United States intervened militarily in Vietnam in the mid-1960s, however, this political consensus began to break down. By 1968, strident debate among American about the Vietnam War signified that the Cold War consensus had shattered, perhaps beyond repair.