Wang Gungwu's 1997 Edwin O. Reischauer Lectures, now published as The Chinese Overseas, traces the experience of the overseas Chinese in the last millennium. By the sixteenth century migration overseas had become a steady current, and in the nineteenth and twentieth centuries, promoted by economic opportunities abroad and politics at home, it became a flood. Whereas the earlier migrants consisted primarily of traders settling abroad, the migrants of the nineteenth century included many manual laborers, and by the twentieth century many were middle-class political and economic exiles. Despite the change in composition, these emigrants retained their Chinese identity.