Yes, the United States sent enough forces to Iraq in order to quell sectarian violence and terrorism during the occupation, because there were relatively few instances of violence. Compared to Iran and Afghanistan, Iraq is in comparatively good shape. Their people generally get along, and the hate towards the United States is not as strong.
Yes, the United States sent enough forces to Iraq in order to quell sectarian violence during the occupation, because the forces that were sent were quite effective. In Iraq, there is diversity of ethnicity and there is diversity of thought. These should not be seen as bad things, because America has these things as well. Iraq is learning how to embrace diversity.
The United States did not send enough forces to Iraq in order to quell sectarian violence and terrorism during the occupation. This is a huge job that no amount of soldiers could take care of. People in Iraq say that they have been set back hundreds of years by the occupation and it would take a huge amount of highly trained soldiers to make this better.
It is clear that the United States did not send enough forces to Iraq in order to stop the burgeoning civil war. Rumsfeld's notion of a limited war was incorrect, and he did not anticipate that the war would expand after the ouster of Saddam's government. The Iraqi people have suffered because of this mistake.
It is clear that the United States did not initially send enough troops to Iraq. The violence only stopped after the troop surge, and violence is again beginning to escalate after the Americans have withdrawn. Rumsfeld's plan for a small invasion force was incorrect, and the Iraqi people suffered for it.