PETER Salins’s book Assimilation, American Style † is a labor of love as much as of scholarship. A child of immigrants who became editor-in-chief of City Journal and later professor of urban affairs and planning at Hunter College, he has lived the American Dream. But, as he chronicles in his new book, the dream is being challenged by ideologues on the left and right. The rise of ethnocentricity on the left and nativism on the right is today threatening the American immigration-to-assimilation ideal. Salins’s book describes how the ideal should work, and did work for generations of immigrants like himself, and decries the new assault that would split American society into tribes and bar additional immigration.