Birthright: The Book of Man
Mike Resnick
 Birthright spans a timeline of nearly 17 millennia, beginning at a very early stage of expansion from Earth and ending with the death of the last humans. In between, it chronicles a slow but (despite some set-backs) steady conquest of the entire galaxy - inhabited by thousands of sentient alien races, which are overpowered and oppressed using whatever tool it takes: economic pressure, diplomatic finesse, or simple military power. Not all chapters deal with mankind's treatment of aliens; some also cover the "internal" politics that result in a development of the growing human empire from a democracy to a monarchy. But the biggest theme is undeniably the search for the elusive quality that allows mankind to overcome all opposition and manage the unique feat of conquering the entire galaxy. It is never clearly defined but manifests perhaps most succinctly when it also results in the failure of an attempt to cross the void between galaxies. Then, after there is no more room for conquest, the only way left is down: internal struggles as well as deep-seated resentment of aliens result in a decline of human power that takes nearly as long as the rise, but is described far less extensively. Somehow, despite whatever enabled humans to achieve total power, they were unable to keep it. Displaying a particular brand of irony, one of the chapters reveals the "literary genre of fiction" as another of mankind's peculiarities, not shared by any alien race.