The Saga of Pliocene Exile influenced Galactic Milieu Trilogy

Julian May's Galactic Milieu is set in the same world as her Saga of Pliocene Exile and written as its prequel: it tells how humanity joined the galactic civilisation and how the Metapsychic Rebellion led by Marc Remillard failed, which is why Marc and the rebels are found hiding in the Pliocene in the earlier books.