Much in the way a company's stock price instantly reflects a hundred different contributing factors (profit margin, executive competence, market outlook, etc), the violence levels in Iraq are an instant indicator of much larger, sweeping trends in the conflict.
The graphic above comes from the Department of Defense's quarterly report to Congress on Iraq. As you can see, we missed the big surge in violence of 2007. We will be entering a country where the federal government is struggling to assert itself over all manner of tribes, militias, and political parties, all while maintaining a semblance of democratic even-handedness. This hasn't worked so far anywhere in the Arab world, but that doesn't mean they shouldn't try. Pray for Iraq.