VDH considers the question:
Given that the United States fields the costliest, most sophisticated, and most lethal military in the history of civilization, that should be a silly question. We have enough conventional and nuclear power to crush any of our enemies many times over. Why then did we seem to bog down in Vietnam, Iraq, and Afghanistan? The question is important since recently we do not seem able to translate tactical victories into long-term strategic resolutions. Why is that? What follows are some possible answers....The real answer is that we don't articulate a strategy because we don't have one that is palatable to the American people. Most of our actions are not in the American national interest, so naturally the objectives underlying those actions can't be explicated in a simple and straightforward manner because they would be rejected. There was no national interest at stake in Iraq, in Afghanistan, in Somalia, in Serbia, or in Uganda. There is none in Iran. And where there is no coherent and strictly delineated objective in the national interest, there is no strategy, and where there is no strategy there will be no victory regardless of the tactical excellence.
The most obvious answer is why we argue over the results of our interventions is an inability to articulate our strategic objectives—what exactly do wish to see follow from our use of force and for how long and at what cost? Do we wish to rid the world of Bashar al-Assad? We could do that quite easily and probably without ground troops. But would the region be more or less stable? Would Iran suffer a blow or find ways to fund more terrorists? Would the collateral damage from funding insurgents or bombing be worse or not as bad as the current Assad toll? Would the insurgents prove reasonable, or more like those in Egypt and Libya—or even worse? Many of our problems seem to hinge on explaining to the public what we wish to do, why so, how, at what cost it is to be accomplished, and what we want things to look like when we’re through.