Please answer a question about the following article about Korean War:

As an initial response, Truman called for a naval blockade of North Korea, and was shocked to learn that such a blockade could be imposed only 'on paper', since the U.S. Navy no longer had the warships with which to carry out his request. In fact, because of the extensive defense cuts and the emphasis placed on building a nuclear bomber force, none of the services were in a position to make a robust response with conventional military strength. General Omar Bradley, Chairman of the Joint Chiefs of Staff, was faced with re-organizing and deploying an American military force that was a shadow of its World War II counterpart. The impact of the Truman administration's defense budget cutbacks were now keenly felt, as American troops fought a series of costly rearguard actions. Lacking sufficient anti-tank weapons, artillery or armor, they were driven back down the Korean peninsula to Pusan. In a postwar analysis of the unpreparedness of U.S. Army forces deployed to Korea during the summer and fall of 1950, Army Major General Floyd L. Parks stated that "Many who never lived to tell the tale had to fight the full range of ground warfare from offensive to delaying action, unit by unit, man by man ... [T]hat we were able to snatch victory from the jaws of defeat ... does not relieve us from the blame of having placed our own flesh and blood in such a predicament."

Who was forced to retreat back to the Pusan Peninsula due to unpreparedness?
American troops