Two Interstellar Civilizations

Poul Anderson's Terran Empire and Julian May's Galactic Milieu are two multi-species, interstellar civilizations with faster than light travel. The human race rules the Empire whereas it has only recently been inducted into the Milieu. However, humanity:

is specially favored by the superior Lylmik race;
will become more powerful than the other Milieu races;
will rebel against the Milieu -

- and, thanks to time travel, there is a unique relationship between the leader of the Metapsychic Rebellion and the chief Lylmik.

Thus, both series perpetuate the old American sf premise that humanity is not insignificant but instead will play a leading role on the galactic stage. Anderson, of course, also explored other options.