That's the conclusion of Frederick Kagan, a military historian writing in the pages of the Weekly Standard (link via OxBlog). The key section:

We have already seen how chaos and civil war in Afghanistan in the 1990s provided the breeding ground for terrorists and a haven for the bases where they trained. If U.S. forces are reduced or withdrawn too soon, similar conditions in Iraq will nurture the al Qaeda operatives of the future. The U.S.-led attack could end up bringing about the very threat that prompted it in the first place--the proliferation of Iraqi weapons to terrorist organizations--if we do not finish what we have begun by establishing a stable and peaceful regime in Iraq.

This will not be accomplished, however, without the prolonged deployment of significant numbers of American ground forces. Smart weapons cannot keep peace. They cannot get schools and hospitals running, or keep electricity and water flowing, or keep hostile neighbors from attacking one another, or provide a police presence to deter looters and criminals, or hunt down and capture individual terrorists, interrogate them, and learn from them the nature of the organizations to which they belong, or find traces of a WMD program hidden carefully in a country the size of California. Only soldiers and marines can accomplish these tasks, and, given the size and complexity of the country, only in fairly large numbers. Given the unrest and political chaos that currently engulf Iraq, it is hard to imagine that the United States will be able to withdraw any significant portion of its 146,000 troops from that country in less than a year without compromising our vital objectives....

It is time to stop pretending that the United States can prosecute a war on terror, conduct peacekeeping operations in Iraq, Afghanistan, Kosovo, and Bosnia, and maintain the security of the homeland without a substantial increase in the size of the armed forces. General Shinseki, the recently retired Army chief of staff, warns us to "beware the 12-division strategy for a 10-division army"--and even he understates the problem. In truth, the armed forces need an increase in size of at least 25 percent.

This problem is not going away anytime soon. The war on terrorism requires statebuilding, which requires large numbers of personnel on the ground. Demands for intervention will not be going away anytime soon, as the case of Liberia demonstrates.

My five-cent analysis is that the problem here is that Rumsfeld has paid far more attention to altering the warfighting doctrine than to the resources and training needed for postwar statebuilding. As I noted ten weeks agohere, the administration seems to have boxed itself into a corner on this issue.

Developing....

UPDATE: I'm pretty sure the U.S. doesn't need to allocate so much manpower for this assignment.