Federal grants drive the militarization of police departments in America.

[octoberlib]

39. Good article on the subject by Jamelle Bouie

This process ramped up with the “war on drugs” in the 1980s and 1990s, as the federal government supplied local and state police forces with military-grade weaponry to clamp down on drug trafficking and other crime. And it accelerated again after the 9/11 attacks and the wars in Iraq and Afghanistan, when the federal government had—and sent—billions in surplus military equipment to state and local governments. Since 2006, according to an analysis by the New York Times, police departments have acquired 435 armored vehicles, 533 planes, 93,763 machine guns, and 432 mine-resistant armored trucks. Overall, since Congress established its program to transfer military hardware, local and state police departments have received $4.3 billion worth of equipment. Accordingly, the value of military equipment used by these police agencies has increased from $1 million in 1990 to $324 million in 1995 (shortly after the program was established), to nearly $450 million in 2013 http://www.slate.com/articles/news_and_politics/politics/2014/08/police_in_ferguson_military_weapons_threaten_protesters.html