This short New Yorker article by Steve Coll is worth reading for, among other things, some interesting statistics:
In 2004, James D. Fearon, a political scientist at Stanford, published a study, “Why Do Some Civil Wars Last So Much Longer Than Others?,” in which he and a colleague analyzed scores of civil wars fought between 1945 and 1999. … two discouraging findings stand out. In 1945, many civil wars were concluded after about two years. By 1999, they lasted, on average, about sixteen years. And conflicts in which a guerrilla group could finance itself—by selling contraband drug crops, or by smuggling oil—might go on for thirty or forty years. The Revolutionary Armed Forces of Colombia, or FARC, has been around since 1964, sustained in no small part by American cocaine consumption.
The good news is that we are stronger than most insurgents; the bad news is that it doesn’t matter:
From the American intervention in Somalia, in 1992, through the French intervention in Mali, in 2013, industrialized countries have been able to deploy ground forces to take guerrilla-held territory in about sixty days or less. The problem is that if they don’t then leave, to be replaced by more locally credible yet militarily able forces, they invite frustration, and risk unsustainable casualties and political if not military defeat. This has been true even when the guerrilla forces were weak: the Taliban possesses neither planes nor significant anti-aircraft missiles, yet it has fought the United States to a stalemate, and the advantage is now shifting in its favor.
William Lind has argued convincingly that only local forces can defeat insurgencies, since legitimacy is too important a factor, and outsiders have to go home eventually.
There do seem to be more aimless wars that never quite end, probably because they are aimless. I was just thinking that there has been some sort of conflict in Lebanon for all but the first six years of my life, and I am 45.