The CoDominium series:
The point of departure of Pournelle's history is the establishment of the CoDominium, a political alliance and union between the United States of America and a revitalized USSR. This union, achieved in the name of planetary stablility, reigns over the Earth for over a hundred years. In that time, it achieves peace of a sort, as well as interstellar colonization, but at the price of a complete halt in research, development, and political evolution.
Corruption and social decay force the CoDominium's BuReloc (Bureau of Relocation) to forcibly transport people from Earth to offworld colonies. This mass expulsion is made possible by the Alderson Drive, a device that allows instantaneous travel across distances of light-years. The starlanes are patrolled by the CoDominium Armed Forces, an elite fighting force created from the French Foreign Legion. The Navy, in particular, sees what the politicans and common people of Earth do not: that Earth is headed for disaster, and their primary mission is to remove as many people from Earth as possible before the holocaust.
In due time, the CoDominium collapses under mounting nationalism worldwide. The United States and Soviet Union each regain their desire for world supremacy; the nations of the Third World chafe after years of CoDominium oppression. The inevitable result is the Great Patriotic Wars, the long-delayed Third World War that begins and ends with massive nuclear exchanges. Much of Earth is devestated; civilization collapses there, and much of the surface is rendered temporarily uninhabitable.
Before the end, the CoDominium Fleet evacuated their families and children from Earth; they plant them at the colonies of Sparta (for the American and European families) and St. Ekaterina (for the Russian and Asian families). Within a few years, the Fleet has sworn allegiance to King Lysander I of Sparta. Sparta and the Fleet soon begin the Formation Wars, taking advantage of the political, economic, and technological vacuum caused by the collapse of Earth to weld the human colonies into a unified government under Sparta's rule -- the Empire of Man.
For several hundred years, the Empire is the sole government of humanity. It is overthrown by the forces of the planet Sauron, who secretly engage in massive genetic engineering to create a race of perfect soldiers -- the Sauron supermen. The Saurons are defeated in their aim of conquering the Empire, but the strain seperates the Empire into many polities. Interstellar trade and travel decline.
In the thirtieth century, Lysander IV of Sparta proclaims a Second Empire, and begins negotiating or fighting to unify the human worlds once more. Many worlds quickly accept; others, known as outies, continue to resist the Empire's hegemony. Against this backdrop of renewal and conflict, humanity makes its first contact with another intelligent, spacefaring species -- the Moties. After initial difficulties, the contact between the two speices would have dramatic impacts on both the Empire and Motie civilization.