This is covered in the FAQ's
http://www.reddit.com/r/AskHistorians/comments/xepyl/what_caused_the_us_and_britain_to_have_such_a/
http://www.reddit.com/r/AskHistorians/comments/zi9n2/can_someone_explain_how_the_united_states_and/
http://www.reddit.com/r/AskHistorians/comments/vjwqy/when_did_the_us_and_britain_become_friends/