You don't have to believe me, but we certainly have the military capability of taking on all those others you have mentioned.
You are mixing the military campaign with some new requirement to nation-build afterwards.
We DON'T have to get involved in nation-building. It was not my first choice in Iraq. I would simply have knocked them off and any other successive government that continued to attack us. After a while, one would have come along that wanted a bit of longevity.
But, I'm not the President and he saw value in an eventual democracy in the middle of the fertile crescent, and he saw value in drawing islamo-fascists to Iraq to fight them.
That's part of the equation. We can't afford for Iraq to become like Afghanistan or Somolia, a power vacuum allowing bona fide terrorists to operate with impunity. Once you take out their only real government, well, you broke it, you bought it.