A study of the peoples who make up America and the groups they formed reveals the altering of the groups themselves in consequence of Twentieth Century events. The turn of the century found an America with a heritage of expansion -- a social and spacial nobility that attracted and affected immigrants according to background. People defined by color organized against pressure; national groups emerged from local in the Italians and started from the beginning among the Greeks; Jews shifted from national to cultural-religious associations; holidays merged as free society sought adjustment. World War I played on heightened ethnic loyalties which were united in an Americanism still wary of foreigners, as evidenced by the red scare and Immigration Law of the postwar era. Depression curtailed immigration and brought impersonal professionalism to once voluntary agencies. A decade of global war and its aftermath of ever-present danger and high prosperity transformed the position of the minority groups, produced a nationalism less exclusive in character, and placed heritage as a means of locating oneself in the Twentieth Century world. This is the tenor of Mr. Handlin's book, apt but not insistent in its expression.