One strain of historical thought that achieved popularity in the 1950s forwarded the notion that immigration - more than the frontier experience, or any other specific event or factor - had been and continued to be the defining element of United States history. In this depiction, the 30 million immigrants who entered the country between 1820 and 1900 had common experiences regardless of their national, religion, or race: namely, in experiencing hardship and alienation, they themselves changed, but they also carried on the development of the nation itself.
Both casual and formal students of history should, however, be careful in equating the experiences of different groups of immigrants, especially under the somewhat blurring concept of "hardship." The description that all immigrants experienced hardship and immigration fails to account properly for the fact that in the 17th and 18th century millions of Africans were forcibly shipped to the United States and sold into slavery. While this group of people should not be excluded from any full reckoning of the nation's migrants, its alienation and hardship was of a substantially different character from that of the other populations, who migrated more willingly and independently and who arrived under and lived in vastly different conditions. If it is, indeed, the degree of hardship and alienation experienced by the different groups of our nation's migrants that have above all shaped both themselves and their nation, then to ignore these distinctions would be to distort an important element of what our nation has been shaped to be.