A young child dies in Norwich, Connecticut, in 1742. His name: Benedict Arnold.
Flash forward 35 years. Without Benedict Arnold, the Americans lose the Battle of Saratoga. Burgoyne continues south, seizing Albany and continuing south. New England is cut off from the rest of the colonies. France does not join the Americans.
Despite furious fighting from other great American generals (i.e. Nathanael Greene, Daniel Morgan, Anthoy Wayne, George R. Clark), the Americans lose the war. Almost all of the revelutionaries either: A) leave the American colonies, heading west (like in For Want of A Nail) or B) are granted amnesty. A couple, like George Washington, are executed.
Probably a later, successful rebellion in the early 1800s. Anti-British feelings abound in the American Republic of today. Probably closer allies with, say, Germany or Russia, rather than Britain or France.