The American Zone by L.Neil Smith
THE AMERICAN ZONE is the story of Win Bear, a detective who discovers a portal - the probability broach - to alternate worlds. Win has settled in the North American Confederacy on an alternate world where George Washington was shot, sending history in a very different turn. Someone is bombing buildings, many people are being killed, and the libertarian paradise of the Confederacy is threatened. It's up to Win to find those behind the violence and stop them before more people die. He'll find adventure, excitement and danger aplenty before he brings the guilty to justice and restores peace and tranquility to his adopted world.