The Glorious Empire
On September 22nd, 1853, the entire world changed. A purple film surrounded much of Europe, Africa, and Western Asia. Only Britain, Prussia, parts of Russia and Austria, and Scandinavia were spared. The rest, up to and including India and all of Africa beyond the Congo, glowed purple and were impassable.
On September 23rd, the film cleared, and in its place stood the greatest Empire the world has ever seen, the bastion of civilization, Rome.
In Constantinople, Emperor Theodosius LXVI was concerned. He was convinced this was the work of the Mongol-Aztec alliance, which had sought to snuff out the light of Roman civilization for decades.
An attack was immediately ordered on the Aztec outpost of Britain. The British tried to resist but they were met with 1500 GALLONS OF GREEK FIRE dumped from glorious imperial airships. By the time the Romans had realized what was going on, the British had already surrendered.
Meanwhile in the United States, drastic measures were taken. A mysterious man from the future who identified only as "The Yank" came with many AK-47s to be used against the Roman Imperials. Lord Jesus Christ descended from the heavens with George Washington to lead the Americans. Instantly American scientists had figured out how to create atomic bombs, vaccinate, make Panzer tanks (but ONLY Panzers!), and generally advanced technology 90 years.
They needed all the help they could get. Realizing that their beautiful steampunk empire was decades ahead of the rest of the world, the Romans struck at the rest of the world- East Asia, Oceania, Africa, and North America.
The stage was set for a battle to determine the fate of the world. At this point I, the author, feel the need to point out that at the time of this war, there was a lot of woman on woman sex going on. Just a lot. So much so that if I were to write a book about it, I'd spend most of the time just describing the sex. But I'm not, so I won't.
Also, when you weren't paying attention, Sealand managed to take the Congo and are now fighting the Romans too.