Maybe this is news to Europeans, but we Americans know that the constant wars are about propping up the military-industrial complex. The US economy is partly propped up by US spending on weapons from private defense contractors. For this reason, presidents and other political leaders never want to push to reduce the military budget, partly because of lobbying from the defense contractors, and partly because they are afraid that reducing the budget will literally crash the economy. Take all that together, and you see the US's perverse incentives to always have a war going on, so they can justify the military spending.
As President and former General Eisenhower said during his farewell address in 1961:
A vital element in keeping the peace is our military establishment. Our arms must be mighty, ready for instant action, so that no potential aggressor may be tempted to risk his own destruction. . . . American makers of plowshares could, with time and as required, make swords as well. But now we can no longer risk emergency improvisation of national defense; we have been compelled to create a permanent armaments industry of vast proportions. . . . This conjunction of an immense military establishment and a large arms industry is new in the American experience. . . .Yet we must not fail to comprehend its grave implications. . . . In the councils of government, we must guard against the acquisition of unwarranted influence, whether sought or unsought, by the military-industrial complex. The potential for the disastrous rise of misplaced power exists and will persist.