Von Clauswitz famously said that one way to win a war is to convince the enemy to stop fighting. He went on to say that the destruction of the enemy’s armed forces is necessary. He was not talking about a major defeat on the battlefield. He was talking about the complete destruction of those forces.
The US has won two wars by destroying the enemy’s forces and then lost those wars in short order by failing to convince the enemy to stop fighting. Vietnam was the first. When Nixon pulled us out of Vietnam the North had been reduced to less than four understrength divisions down from over a hundred at the height of the 1968 Tet Offensive. Within five years of the US pull-out the North savagely defeated the South uniting the country under one government. In effect, by not convincing the North to stop fighting the US snatched defeat from the jaws of victory. Of course the American people were not willing to support the necessary actions to destroy the will of the North even though we had destroyed their armed forces.
The second time we snatched defeat from the jaws of victory is in the current conflict in Iraq. (Afghanistan is still an open question at this writing.) We destroyed the Iraqi army, but failed to recognize the real enemy: Jihadists. By this failure and by US actions following the initial victory, we can see that the will to fights was never seriously challenged. Thus the rise of ISIS and the current destruction of both Iraq and Syria.
What’s the point? Modern warfare is asymmetric in that ridiculously under-armed forces continue to fight in whatever manner possible to them while equally ridiculously over-armed forces are helpless to gain a decisive victory. By decisive I mean a victory that would challenge the will to fight.
The Jihadists have been fighting each other for more than a thousand years. Never once has there been peace in their part of the earth because they were never able to seriously challenge the will of their various religious sects to fight. Such a challenge is difficult to arrange when the fight is over issues more properly related to the afterlife than to the life in the earth.
It is axiomatic since Clauswitz that victory requires the victor to eliminate the vanquished will to fight. All the depredations of war, all of the terrible consequences have this one purpose — to force the enemy to stop fighting. There are only three ways to do this. First you may assimilate the enemy into your own culture.
Failing that you may enslave through conquest the enemy by force of arms.
Failing that you are left with the option of killing all members of the enemy camp, military, militia, and civilian.
Our current enemies refuse assimilation. Our current friends refuse to enslave by conquest. There can be no victory in the war against the Jihadists until we kill all of them, military, militia, and civilian.