I read something about one of the reasons the police have become more militarized and it wasn't the reason I expected (I'll see if I can find the article and link it). It had to do with city budgets and the way they were pushed out and continued. The gist of it was, the police had to allocate spending their budget within a short time frame or the budget they had would be put into the cities "general fund" (I believe this was Seattle, as that's where I live... mileage may vary). The next year's budget would be reduced to reflect the lack of spending. In order to reduce the risk of not having enough resources, police departments would make sure to spend all of their remaining money on 'necessary' equipment for their units. They could get A LOT of military equipment for a good price because of our 20 odd year wars over season, and our love of specialized units in the police departments, it was a match made in heaven.This type of short sighted, feast or famine spending coupled with readily available surplus military equipment has lead to an ever increasing militarization of the police that has a less effective, effect on community policing and crime, statistically. But all of this is because of how our government handles its accounting practices and sells its surplus military gear.

I think I heard it on Freakonomics, but I'm not sure.