The 18th century in America was marked by two kinds of imperialism: the British, French, and Spanish doing battle with each other; and all of them pushing against the Native Americans who weren’t allied with them. But was the effort to take land from the Native Americans really imperialism? After all, virtually all of it was driven by settlers, not the governments of the mother countries or the colonies, and there was no real attempt by either the British or French colonists to exploit and rule the much-diminished native population, whom the British settlers just wanted to go away, one way or the other. Morally speaking, that may not be an improvement over imperialism, but it doesn’t fit my definition.
Anyway, the British Empire prevailed over the French version in the French and Indian War, and the French relinquished their rights to North America. The British government, far from encouraging the colonists to take Native American land, imposed a limit on it with the Proclamation of 1763. This in turn was one of the most important colonial grievances that resulted in the Revolutionary War.
At the end of the 18th century, both American political parties recognized that settlers would ultimately control all of the land east of the Mississippi. The Federalists were unenthusiastic about the process and wanted to keep it slow and organized; the Republicans were far more bullish about the expansion of “civilization.” The Native Americans, for their part, were in deep trouble, and the American colonies were still bordered by Spanish possessions to the south and west.