In those days, when the U.S. "left" one of its imperial experiments, it left. In Vietnam, this was because the other side "won". Ditto Laos and Cambodia.
These days we don't seem to ever get out. Having kicked the hornet's nest, we stay on but pretend the troops we leave in place aren't in combat. A Marine was killed in northern Iraq last week. In January, a U.S. soldier died in Marjah, Helmand province, Afghanistan -- an insignificant place which has suffered from U.S. attention off and on since 1946. Rajiv Chandrasekaran told that story.
ISIS is a plague on the planet. Any responsible government would be trying to eradicate it. The terror of terrorism makes us stupid and mean, as it is intended to. What we need is to be smart and brave. That's hard, but it is the only stance that is going to preserve healthy communities and states.
Oddly, the billionaire George Soros, himself a refugee from Nazi barbarism before he took up crashing currencies for profit, understands this as well as anyone.
We can't fight ISIS by demonizing Muslims or shutting our borders to refugees. The challenge that confronts the generation that Feels the Bern is not only to take our communities back from the plutocrats, but also to demonstrate that it is possible to build a society where people of all colors and all faiths can work together for the common good. That's the true threat to the terrorists -- and also to the plutocrats.