One of the biggest is the fact that Police Officers in the US pledge an oath to the people of the US and the Constitution. Other police agencies do not, and usually don't carry guns like their American counterparts. American Law enforcement relies on the judgement of the officer who also has to abide by rules and regulations, but are mostly able to judge a situation how they want.
Another big principal that is controversial... American Law enforcement are Public Servants, which means they serve and are ruled by the public and not the federal government.
