Why is the U.S. Army Chief of Staff warning against 'little green men'?

"You'll be dealing with terrorists, you'll be dealing with hybrid armies, you'll be dealing with little green men, you'll be dealing with tribes, you're going to be dealing with it all, and you're going to be dealing with it simultaneously," United States Army Chief of Staff Gen. Mark Milley said in a speech last week at Norwich University.

Ummm… what?

Milley's comment fueled conspiracy theories across the Web.

The Army later weighed in though.

"It does not mean fighting troops from outer space," the officials said. According to the Army Times, "The phrase 'little green men' typically refers to foreign troops or paramilitary forces who dress in green attire instead of traditional military gear."