The Unification Wars were a series of conflicts fought on Terra during the 30th Millennium at the end of the Age of Strife. It was during these campaigns that the Emperor of Mankind first publicly revealed himself to a desperate humanity and began his conquest of Terra to unify the techno-barbarian nations that dominated the sacred homeworld of Mankind and forge the foundation of the Imperium of Man.
By the time of the Unification Wars there was only one remaining ocean on Terra -- the so-called Great Ocean -- which was the ancient Pacific Ocean. The size of the Pacific was vastly smaller than it once was, due to the vaporisation of a massive stretch of the ocean during the nuclear wars that had consumed much of Old Earth in the lost years of the Age of Strife. This missing portion of the Pacific stretched from the Marianas Trench down past Australia and all the way to the frozen continent of Antarctica. The Atlantic Ocean had also been largely vaporised as the great body of water that had once been near Europe was now mostly gone, particularly to the south of what had been the Iberian Peninsula.
The greater empires at the time were:
Corresponds to 20th century America and Canada. Source of the Iron Warriors. Calbi or Great Albia was a vassal to Merika.
Corresponds to 20th century USSR. Led by warlord Kalagann. In Horus Rising, Kyril Sindermann lends Loken a copy of the Chronicles of Ursh. Ursh was the mightiest empire on Terra before the Unification and therfore the biggest enemy to the Emperor's forces of Unity.
Corresponds to South America. Ruled by Dalmoth Kyn. Hy Brasil is ruled from the Planalto, a massive Hive Conurbation - the Goverment is based in the Sao Paol part. The Palanto draws its power from 'a series of vast reactors buried in the heart of the main conurbation', whose heat exchange processes mean that the reactor district is 'caked in thick sheet-ice all year round, forming a gigantic frost park thirty kilometres square'. This area is known as the 'Winter Fields' and is used for recreation by local inhabitants.
Pan Pacific Empire:
Corresponds to east Asia and Australia. Led by half mad half genius Tyrant Nathaniel Dume. He was eventually defeated by the forces of the Emperor during the Unification Wars, removed from power and imprisoned within the great Imperial prison of Khangba Marwu, releasing his people from their oppression.
Corresponds to Indonesia and southeast Asia. Led by Cardinal Tang. He wished to 'return the world to a pre-technological age', burning 'scientists, mathematicians and philosophers' who opposed his Church's views. He also killed millions in pogroms and death camps in an attempt to secure racial purity.
The Antarctic Powers:
Corresponds to Antarctica
Skand or the Nordyc:
Corresponds to Scandinavia. Source of Space Wolves.
Gredbretton / Albyon:
Corresponds to England. Its ruling tyrant was named Uilleam the Red was known to drink human blood. After his defeat by the forces of the Emperor, Uilleam was imprisoned in the Imperial prison in the Himalayan Mountains known as Khangba Marwu, The Vault.
Corresponds to northern France. Havuleq D’agross was the last independent ruler of the Franc, leading a rebellion against Imperial rule and killing the Emperor's appointed governor. His rebellion began in Avelroi, but rapidly spread until he could muster a force of 50,000 rebels, largely unskilled militia. They eventually fought the Emeror's armies at Gaduare, 'a line of high hills' buy the ruins of Guaduare Bastion. There they were wiped out by a force of less than 5,000 Imperial troops, including proto-Space Marines.
Corresponds to south central Europe, including southern France, Italy, Austria, and Yugoslavia. Source of the Emperor's Children.
Corresponds to Egypt
The North Afrik Conclaves:
Corresponds to Algeria and northern Africa
Timbuk and Nama Gola:
Other nations in Africa
The Quintiple Alliance:
Fringe of countries to west of Ursh, such as Jermanic (Germany), Terrawatt Clan, Uralia, and Achaemenid Empire (Mesopotamia). Achaemenid Empire is the source of the Thousand Sons.
The Emperor's Children, or IIIrd Legion, was created alongside its brother Space Marine Legions during the latter phases of the Unification Wars, with many of its finest warriors drawn from the courts and blood vassal populations of Europa.
The nobles of Europa selected the finest of their youth and offered them up to the Emperor of Mankind as tribute and penance for their previous defiance after their systematic humiliation in battle at the hands of the Imperial Thunder Regiments. Among them were sons drawn from each noble family, a fact apocryphally said by some Imperial savants of the time to have given the Legion its lasting name, reaffirmed in later years by its Primarch after his rediscovery by the Expeditionary Fleets of the Great Crusade.
Of this tithe some Europan noble familes gave in grudging tribute, and thought of these young men as little more than hostages, while others cooperated with the zeal of true converts to the Imperial cause. House Loculus of Komarg is said, for example, to have sent all of its sons to be transformed into Astartes at the time of their capitulation to Imperial rule, and to have given the firstborn son of each generation thereafter to the IIIrd Legion willingly.
In later decades, other Terran dynasties followed the example of Europa, filling the ranks of the IIIrd Legion with the flower of Terran youth who seemed well-matched with the aristocratic blood of its Initiates, forming a martial brotherhood whose ancestry in war stretched back into the lost ages of human history.