If you check out the US entry in the CIA World Factbook, you will see that we are listed as a Constitution-based federal republic; strong democratic tradition.
Federal republic - a state in which the powers of the central government are restricted and in which the component parts (states, colonies, or provinces) retain a degree of self-government; ultimate sovereign power rests with the voters who chose their governmental representatives.
Now, when this country was first created, it had thirteen former colonies that had very different cultures and ideals. None of these newly declared states wanted to totally give up their rights of self-government to a central government. They wanted to be able to decide certain things themselves. If those people on the other side of the state line wanted something different - more power to them.
But there were worries that a strong federal government might override the states' sovereignty by using the excuse of an emergency to come in and take control. And actually, JFK sort of did this in 1963 against Gov. George Wallace, ordering the governor's own National Guard to turn against him and forcibly integrate the University of Alabama. Of course that was to uphold a federal mandate. In the case of looters, who are breaking no evident federal law, the Posse Comitatus Act of 1878 explicitly forbids using the military (unless a governor uses her National Guard under "state status") in a domestic police function.
What this means is that according to the law, the STATES are given the chance to solve the problem themselves FIRST. The federal government is not allowed to step in without the governor's permission. After all, the governor is supposed to have a better idea of what the citizens of his state are in need of than the feds in Washington D.C. Only when the state government cannot handle a crisis that the feds have the right to step in. Theorhetically, a president could get impeached for infringing on a state's sovereignty - that would indeed be seen as a move towards dictatorship.
This part of the reason I get so disgusted with the ignorant people make comments about any president having dictator-like powers. The state governors have powers that keeps this from happening. But if we keep insisting that the federal government fix everything immediately, then we weaken that check and balance. Of course, there is something in place when the governor does screw up and the president should step in then, but we shouldn't be so surprised when they don't step in immediately. Presidents who have done so in the past always get flack for doing it, no matter what their political party.
I'm not saying that everything worked like it should recently. In fact, I think there were major screw-ups on all levels and Brown deserved to be removed. I just don't want us to forget why we let the states ask for help from the feds, instead of the feds just moving in like an overbearing parent and making everything right. It's not supposed to be a parent/child relationship between the federal government and the state governments. They are supposed to be more of less equals. If you are a competant adult, you don't want someone else barging in when you have a problem unless it's an emergency you can't handle. That's true for the states too.