With the UN military situation in Korea improving in early 1951, President Harry S. Truman was contemplating offering a peace negotiation to Communist China.
However, in late March 1951 General Douglas MacArthur independently challenged China to admit defeat, thereby simultaneously challenging both China and President Truman. Truman’s proposed peace negotiation announcement was then shelved.
In April 1951 the Republican leader in the House of Representatives read aloud a letter from MacArthur that was critical of Truman’s Europe-first policy and limited-war strategy. The letter concluded with:
It seems strangely difficult for some to realize that here in Asia is where the communist conspirators have elected to make their play for global conquest, and that we have joined the issue thus raised on the battlefield; that here we fight Europe’s war with arms while the diplomats there still fight it with words; that if we lose the war to communism in Asia the fall of Europe is inevitable, win it and Europe most probably would avoid war and yet preserve freedom. As you pointed out, we must win. There is no substitute for victory.
In April 1951 President Truman relieved General MacArthur of his command.
In 1956 President Truman wrote: If there is one basic element in our Constitution, it is civilian control of the military. Policies are to be made by the elected political officials, not by generals or admirals. Yet time and again General MacArthur had shown that he was unwilling to accept the policies of the administration. By his repeated public statements he was not only confusing our allies as to the true course of our policies but, in fact, was also setting his policy against the President’s… If I allowed him to defy the civil authorities in this manner, I myself would be violating my oath to uphold and defend the Constitution.
General Source: Wikipedia