In a sense, American isolationism is as old as the nation itself. The first colonists who separated themselves from Europe--whether to escape religious or political oppression or economic hardship, or simply to make a profit or to satisfy a quest for adventure--in effect accepted the prospect of a life of virtual isolation from the Old World.
This separation from Europe, of course, was never complete. The early colonists were almost totally dependent on their mother countries for supplies and protection. And colonial American accepted and appreciated that their civilization in the New World was largely a product of the Old. In the late colonial period, American aristocrats traveled to Europe, modeled their fashions from those of Europe, and sent their sons to the best European universities. Until the very eve of the Revolution, Americans considered themselves Englishmen who had been transplanted to the New World.
It is also true that Americans who accepted independence from England did so only reluctantly, so strong were the bonds with the mother country. Even after independence, the former American colonies maintained important economic ties with the nations of Europe, and their cultural roots in the Old World continued to be fertilized by waves of new immigrants who helped account for the rapid growth and development of the new nation.
Nevertheless, the first settlers in America came to realize keenly that distance in space and time separated them from Europe, and that this separation had made them different from Europeans. To survive in their new environment, Americans began to develop new patterns of behavior and thought that ultimately helped to make them a new nation. It was a nation distinct in many ways from the Old World. Nowhere in Europe was there the degree of tolerance of expression, whether religious or political, that was found in America at the time of the Revolution. In no land was the gap between rich and poor so narrow, and class distinctions so unimportant. In no European country was there the absence of dynastic feuding and warfare that existed in colonial America.