Let me give you guys a clue.
I know this will come as a huge shock to you to learn...
During World War Two, until it's end in 1945, our ENEMIES were the AXIS powers -- i.e., Germany, Italy and Japan. Got that so far? Axis = enemy.
Our ALLIES were the Communists -- especially the Soviet Union, who lost 100 dead for every American soldier killed in battle. In those days, we liked and appreciated the Communists, we didn't consider them our enemies, and we were glad for every Axis Enemy they killed.
Now, of course, you may consider that naive, even wrong headed, but the facts are the facts, and if you don't understand it, then nothing America did in those days can make any sense to you.
Got it?
Things were not quite as simplistic in all respects and all regions as you seem to think they were.
George Marshall didn't betray Chiang until AFTER World War Two [although Molotov was feeding disinformation to Hurley during the war].
Chang & Halliday have an entire chapter on it, called "Saved by Washington" [i.e. Mao saved by Washington], covering the period 1944 to 1947.
Our ALLIES were the Communists
No, in China, our allies were supposed to be the Kuomintang, led by Chiang.
But after WWII, Chiang was betrayed by Marshall & the State Department:
George C. Marshall - Post War: China and Secretary of State
http://en.wikipedia.org/wiki/George_C._Marshall#Post_War:_China_and_Secretary_of_State...In December 1945, Truman sent Marshall to China to broker a coalition government between the Communists under Mao Zedong and America's Nationalist allies under Chiang Kai-shek. Marshall had no leverage over the Communists, but threatened to withdraw American aid essential to the Nationalists. Both sides rejected his proposals and the Chinese Civil War escalated, with the Communists winning in 1949. His mission a failure, he returned to the United States in January 1947. As Secretary of State in 1947-48, Marshall seems to have disagreed with strong opinions in The Pentagon and State department that Chiang's success was vital to American interests, insisting that U.S. troops not become involved...
Patrick J. Hurley - China
http://en.wikipedia.org/wiki/Patrick_J._Hurley#China...Throughout his tenure in China, Hurley felt that his efforts were being undermined by State Department officials, principally John Stewart Service and John Paton Davies in China, and John Carter Vincent in Washington, who he felt were unduly sympathetic to the Communist forces led by Mao Zedong...