Why the United States Needs an Out-Sized Military
As a means of negotiation, a war conducted by rational actors continues until both sides come to a mutual understanding of the other's military strength and willingness to continue fighting. Once this mutual understanding is reached, negotiations will be pursued by both sides and may be satisfactorily concluded.
Military strength and political willingness, though both necessary, may to a certain extent be substituted for the other in a given war. In the Vietnam War, for instance, the Vietcong and North Vietnamese made up for their lack of equipment by a willingness to continue the war for as long as it took. The current U.S. military posture is an example of the other side. We have overwhelming military strength, because we do have sufficient political willingness.
In short, the U.S. needs an out-sized military so it can win a war with a minimum of political commitment. If we face an opponent who can withstand our initial onslaught, we lose.