>>js2+(OP)
The American police force seems to be a catch-all for the vast amount of social problems caused by unequal access to healthcare, limited social security and a host of puritan laws that ignore peoples needs. Making drug users criminals despite the massive numbers of them drives up prices and decreases access causing large amounts of crime out of social problems caused by missing social systems. The drug war has also caused a lot of organised crime on an impressive scale and packed out prisons that treat its prisoners appalling badly, falling very much into the punishing end of the spectrum and addressing very little rehabilitation which reduces reoffence.
Combine all that lacking social programs and support with the culture around guns, which a lot of the populace owns, and you have by necessity a very militant police force. America has a lot of social issues which much of the populace does not want to address and the police end up arresting it all and putting them in prison. It impacts the middle classes a lot less and they don't want to pay for it so as a populace they suffer the consequences of those choices in their schools and criminal gangs and subsequently military-like police. There are other ways to do this but I highly doubt America will choose any of them in the coming decade.