We have all heard the old adage that war is an extension of politics. Carl Philipp Gottfried von Clausewitz was certainly an advocate of that concept. He said, "...the political cause of a war has a great influence on the method in which it is conducted." He also said, "War is the continuation of policy by other means." von Clausewitz defined war: "War is thus an act of force to compel our enemy to do our will." He also saw war, or military force, as an instrument that politicians could use to pursue their policies. I encourage readers to read his book, particularly Chapter 6, which deals with the politics of war.
So why cannot politician, once they have started wars to enforce their policies, back off and let the experts, the military men (and women) fight the war?
While von Clausewitz was correct, politicians, such as Harry Truman and LBJ, could/would not stand back and give the military an unfettered hand. WWII was a war where FDR kept his opinions and policies to himself and let General Dwight Eisenhower have a free hand. Unconditional victory resulted. Then came Korea and Viet Nam. Generals Douglas MacArthur and William Westmoreland were told by politicians HOW (strategy) to fight, resulting in getting many people killed and withdrawal. Now Obama is in (over his head in) Afghanistan, and he wants to dictate policy. Some will (correctly) argue that Obama inherited the Afghan war. So? He still wants to "manage" it, to enforce his policy.
So let's look at what some people who HAVE experienced war (and, IMHO, earned the right to express an opinion) have to say about war. [BTW, in the interest of full disclosure, I was in the Army for 22 years, mostly in NBC, and saw action in the first Gulf war]