In the 18th and 19th centuries, the metaphor of a "crucible" or "smelting pot" was used to describe the fusion of different nationalities, ethnicities and cultures. It was used together with concepts of the United States as an ideal republic and a "city upon a hill" or new promised land. It was a metaphor for the idealized process of immigration and colonization by which different nationalities, cultures and "races" (a term that could encompass nationality, ethnicity and race proper) were to blend into a new, virtuous community, and it was connected to utopian visions of the emergence of an American "new man". While "melting" was in common use the exact term "melting pot" came into general usage in 1908, after the premiere of the play The Melting Pot by Israel Zangwill.
The first use in American literature of the concept of immigrants "melting" into the receiving culture are found in the writings of J. Hector St. John de Crevecoeur. In his Letters from an American Farmer (1782) Crevecoeur writes, in response to his own question, "What then is the American, this new man?" that the American is one who "leaving behind him all his ancient prejudices and manners, receives new ones from the new mode of life he has embraced, the government he obeys, and the new rank he holds. He becomes an American by being received in the broad lap of our great Alma Mater. Here individuals of all nations are melted into a new race of men, whose labors and posterity will one day cause great changes in the world." In 1845, Ralph Waldo Emerson, alluding to the development of European civilization out of the medieval Dark Ages, wrote in his private journal of America as the Utopian product of a culturally and racially mixed "smelting pot", but only in 1912 were his remarks first published. In his writing, Emerson explicitly welcomed the racial intermixing of whites and non-whites, a highly controversial view during his lifetime.