China would definitely be on the move without our presence in the Pacific, Russia and Iran already have their tentacles spreading through the Mideast which would only intensify, and North Korea would likely be storming across the DMZ within days after an American withdraw. For all our faults,the US and its allies are all that keeps the world out of much larger conflicts.
As for Afghanistan, it is not an ideal situation, but I believe Obama has made a far better decision this time around. He has likely learned from his mistake in Iraq where his own administration claimed the conflict to be won, pulled troops from the field, and allowed ISIS to rise up. The military still maintains bases in Germany, Japan, and South Korea for strategic purposes and it appears Afghanistan will just be another on the list. I truly don't like America being the policemen of the world, but someone has to stand in the breach and no other country is capable.