"However you slice it, Afghanistan has gone south in the last few years," says Peter Bergen, senior fellow at The New America Foundation, Afghanistan expert and author of The Osama bin Laden I Know. "It has been a strategic failure for NATO. So many countries have caveats that prevent their soldiers from fighting. There's a complicated chain of command. Domestic opposition won't allow those countries to send more troops.

"That political pressure doesn't exist in the U.S. And there's no denying that America has the most effective armed forces on the planet." LINK