General Douglas MacArthur had fought in the first and second world wars and then in Korea. He had served as General of the Army. The transition from WW1 and WW2 to Korea marked a transition to a different kind of war, from the massive collision between the vast armies of industrial nations to a proxy war fought between the armies of an industrialized nation and guerrilla and insurgent forces supplied and trained by its enemies.
Korea was the first test of such an engagement that would shape the nature of the wars America fought throughout the twentieth century. After much bloodshed and loss of life, the allied nations managed to keep South Korea free, in a prolonged and bloody campaign. The Vietnam War would follow the Korean War, a war in many ways not too dissimilar but one fought by a generation that had seen its culture and its elites heavily infiltrated by the ideology of the Communist enemy.
The War in Iraq we are fighting today is a repetition of the same fundamental problem, a struggle to maintain order and a functioning nation against an insurgency backed, armed and funded by the enemy outside its borders. As China backed North Korea during the Korean War, Syria and Iran have backed the Sunni and Shiite terrorists operating in Iraq.
General MacArthur who had faced the problem at its very beginning in Korea and whose bold strategy at the beginning of the war had brought an early victory, understood what needed to be done to win the war. The Chinese bases inside Manchuria had to be destroyed. Without that the UN forces were faced with cutting off a dragon's head that repeatedly regenerated itself. But such a tactic was not politically correct and so it was denied by Truman, eventually leading to MacArthur's dismissal. The Korean War became a holding action that was only sustained at the cost of much blood.
The continuing War in Iraq, is not a war. The war was fought and won in a short period of time. It is a campaign where US troops have been set to try and maintain order in a country tearing itself apart, in part due to existing tensions, but in great part due to outside interference. The ability of Sunni terrorists to use Syria as a gateway for arms and terrorists gave birth to the insurgency in the first place. Iran's training and arming of Shiite militias and general efforts to touch off a civil war have brought the situation to its current disastrous stage. Iranian forces have openly operated in Iraq. Iranian personnel have been captured in raids. The actions of both Syria and Iran have allowed them to take thousands of American lives while barely lifting a finger themselves.
A proxy war can only be won by either destroying a country or by engaging and defeating the forces using the insurgents as proxies. Everything else at best leads to a stalemate or to defeat. This is the third time the United States has had to learn this lesson and it has yet to be learned primarily because politicians choose to ignore the hard realities of war and ignore the soldiers who speak them.