French and Indian War
England was scared of the colonies uniting and ignoring their authority. New England increased in self-government. The middle colonies relied on grain production and fur trading. The south had slaves for their tobacco, rice, and indigo plantations.
The French and Natives came together to beat England. They wanted the land for easier trade/travel, fresh water, and the good source of food. At first the British were at a disadvantage because they weren't used to the territory, they fought like gentlemen, and they were easy targets. Then William Pitt takes control of British forces and they get a lot better. Colonies are forced to quarter soldiers, join armies, and give supplies.
The colonies united. Britain gains all of France's land east of Mississippi river. Spain lost Florida to Britain but gained Louisiana territory. The war cost England money. They made the colonies pay for half of the costs which started the bitterness between them. The Natives came together and made a rebellion. The Proclamation of 1773 stated that all land to the west is theirs. This didn't last for long.