In the summer of 1846, Great Britain is thriving under the expansion of steam-powered technology, and holds the world's largest militarized airship fleet. They also possess the largest standing military on the planet.
However, the every day citizens are suffering from the smog-filled air, with many dying in the streets daily. The upper echelon of the political structure [i.e, the king and his parliament] pay the citizenry no mind, and, as the major cities become less and less livable, the populace begins to revolt. Riots become more and more common, often repressed through violence. Eventually, the fiefdom begins to hire mercenaries from other countries to quell the rising tide of the populace demanding revolution.
After a ten-year struggle, Great Britain's power structure collapses, and a new king is instated. To deal with the citizens, he appoints a Prime Minister and attempts to level out the industrial plant's pollution so the people can live without fear of dying from disease.
It is now 1859, three years after the end of the English Riots. Seizing the opportunity to conquer a land that's fallen from grace, Prussia (Germany) declares war on Great Britain, occupying most of the country.
The heroes (PCs) start in London, July 1859, spared from the massacre. Most, if not all, weapons have been seized by the Prussian Military, but spies and freedom fighters seek to undermine the occupation and restore their once Great Homeland.