I think it's more militarization of the police because of easy access to guns (so logically police has to have bigger better gear) and erosion of rights followi

I think it's more militarization of the police because of easy access to guns (so logically police has to have bigger better gear) and erosion of rights following 9/11 (and the gradual complacency/acceptance of it). Mix in a long history or racism, easy access to information - stir and wait for it to explode.