Every Option

Adapted Men colonize extrasolar planets and Okies trade with extrasolar colonies. Volume I of Cities In Flight describes the discoveries of anti-agathics and antigravity that made the Okies possible. However, The Seedling Stars, in which Adapted Men spread through the galaxy, is not Volume II of this tetralogy because the two series developed towards different conclusions. See Interstellar Travel. They also acquired different beginnings, making them distinct series, unlike the Haertel Scholium where four futures share a common beginning.

Earth is ruled by:

the Russian Bureaucratic State in Cities In Flight;

an American Port Authority in The Seedling Stars;

a UN where entire cities have become underground "Shelters" in A Case Of Conscience;

a peaceful UN in the Heart Stars novels.

Blish presents four rationalizations of parapsychology, two in the Haertel Scholium and two in independent works. He gives the impression of addressing every option like Poul Anderson with interstellar travel, time travel, aliens and AI.