Sliding Albion is the codename for an alternate universe (as well as said universe's Britain) in which Earth was visited by an alien race nicknamed "the Blues" during the Renaissance.
Despite the vast disparity in technology between humanity and the aliens, there was a unity of purpose between them, leading to interbreeding and an imperialist culture similar to the Victorian British Empire.
Apparently, the alien/human alliance was centered around two poles: England, which kept most of its human royal line, and Italy, which quickly intermixed with the aliens. One of the original Blues, Regis Slzfi, was in a position of power in the Italian faction. For some reason, the Italian/Blue alliance didn't develop so well, and started to grow envious. In such they started late colonial wars against poor countries like Africa or China. As military leaders the Blues were not the ones to hesitate, and they immediately utilized bacteriological and nuclear warfare. After a century or so of such wars, Sliding Earth became so poisonous that life was barely possible. The new territories, thus conquered, saw their population so weakened that the surviving females were not able to stand a Blue crossbreed pregnancy. The Italian Blue were facing a serious birth rate problem. This problem may have existed in Sliding Albion too, but as the country was still ruled by the human Windsor bloodline, it was less critical. Furthermore, Sliding Albion's colonies haven't been poisoned, in which the Blue/Human birth rate was certainly not so critically low. In further expanding the number of Blues, the Blue's leader Regis lead an invasion of China in 1856 (presumably because of its high human birth rate) resulting in having all the country's males killed and the women being used for breeding, turning China into a "rape camp".
By the early twentieth century the power of the hybrids became stagnate, forcing the Blue to search and invade other parallel universes by breaching their universe's barriers and travel through The Bleed. Eventually Sliding Albion made contact with the Wildstorm Universe. This led to only the British government, and partially the American government, in having a secret peaceful foreign relationship between themselves and Sliding Albion. However, the relationship eroded in 1953 and the Sliding Albion reality entered its first World War with a parallel world, and bacterium weapons were unleashed on their London. In a final act of contempt and spite, Sliding Albion vented the bacterial fallout over Britain in a failed attempt to save themselves. However, this agent changed while traversing The Bleed and caused the first surge of superhuman powers in Britain.
Afterward, Sliding Earth witnessed relentless world wars between England and Italy, until the Ninth, where Italy won, and Regis was given the kingship of Sliding Albion.
With the past wars and the bacterial infection in 1953, Sliding Albion's Earth suffered a dramatic decrease in the human/Blue hybrid population in Europe, its society is stagnated, and losing the knowledge of traveling through parallel worlds. By 1999 King Regis restored the Blues' knowledge of shifting through The Bleed and once again have the Sliding Albion empire to invade the WildStorm universe's Earth in his quest in securing the survival of the Blues by having the planet turn into a rape camp. After sending a raiding force into Los Angeles, the Authority defeated the invasion force. However, the Blues re-invade in a massive force over northern Europe. In the efforts of the Authority, Apollo destroyed the entire invading force, the team's Carrier destroys Sliding Albion's Buckingham Palace, Regis is killed by Jack Hawksmoor, and The Doctor destroyed Italy and what's left of the Blues' regime along with it. In an all-frequencies message, Jenny Sparks told the people to take advantage of the second chance to redeem themselves for a better world.
However, following after Armageddon, Sliding Albion re-invade England in a much larger force in retaliation to the death of Lorenzo Antonio Slzfi. The Sliding Albion armada inopportunely arrive during Earth's war against the Knights of Khera and leading into a three-way battle in which they were shortly quashed and repelled by the Kherans.