Marine General Conway basically describes that strategy here:
What I told the troops in Iraq is that the most dangerous thing that our Corps is doing today is happening in Afghanistan. The most important thing we're doing today is happening in Iraq. And that is because we're sealing the win there.
They are making sure that although the clock is ticking down, and we're on the other guys' five-yard line, that they do the right things to close this out.
The reason that we think it's so critically important that we do so is that it's the first battle of this extended war against extremism. Our philosophy has worked.
The idea from the very beginning that we needed to insert a wedge between the extremists and the moderates in the country showed itself, in 2006, when the Sunnis out in Anbar with us rose up and said, we've seen these guys; we know what they do; we're tired of the murder and intimidation and we're going to turn on them; with your help, we will slaughter them.
Their term, and that's what -- that's what started to turn that thing. And we should all find encouragement through that, because that has I think spread itself across other portions of that region. And in a less overt way, other nations are using their security forces to go after some of these same people.
I would also offer that the way we see Afghanistan is very much through the filter of Iraq. And that we come out of Iraq under a victory pennant, facing now what we see in Afghanistan, I think, is the way we would want to do that, the way we would hope and expect American forces to be able to do that.
Since 9/11, we've followed win-hold-win. Initially, Afghanistan was the priority theater and we held against Iraq with our forces enforcing no-fly zones over Iraq and containing Saddam. Once we overthrew the Taliban regime we shifted to Iraq.
While we worked to win in Iraq, the Afghan theater was pretty quiet. We simply didn't face enough of a threat there to even remotely justify the charge that we were distracted by Iraq from winning in Afghanistan. By the end of 2008, Afghanistan was heating up (from sanctuaries in Pakistan and al Qaeda's defeat in Iraq which led them to focus on Afghanistan and Pakistan) even as we saw the beginning of the end of our Iraq commitment. By then, we were holding in Afghanistan while completing the win in Iraq. As we can anticipate dramatic withdrawals from Iraq, we now feel free to send troops to Afghanistan to win that war (with the added problem that we need Pakistan to win their part of the Taliban Campaign for us to really win in Afghanistan).
So win-hold-win will always be our strategy, rather than a sign of distraction or taking our eye off "the ball." The fact is, even when there's more than one ball, we can only focus on one. As long as we are fighting with a basically peacetime-level Army and Marine Corps with only a partial mobilization of reserves and limited generation of new forces, we will be restricted to one major war at a time.