Pre-1945 modernity sought to reduce the human gene pool...

.... while post-1945 postmodernity seeks to preserve the human gene pool.

The elderly Congressmen of 1946 (who had been teenagers in the 1880s) who thought that there could only be one "atomic secret" and that America had it - that was quintessentially Modern.

 Similarly the fact that middle aged voters today (who were teenagers in the 1980s) show a wide tolerance for racial, sexual, physical and cultural variety is quintessentially Postmodern.