Elzevir is a fantastic uchronia. It is not a "realistic" uchronia as I did not bothered with a complete and logical timeline.

The main elements are probably the following. In 1839, a meteor enter the atmosphere and breaks in multiple elements. The biggest fell on england and destroyed a large part of the Midlands. A lot of "small fragments" fell on the rest of the britanic isles. Other rocks and a rain of "small fragments" fell on different locations around the world.
In this regions, a strange and fantastic mist appears, and the meteors brought a radioactive substance called promethium (as well as "eurydyme" and "betylium").
As a result, the British Empire collapsed, and a lot of refugees became part of the French Republic, of the Vesterhaven Concordat or the American Alliance. French Republic and Vesterhaven Concordat seized the major part of the british colonies, India became independant.

Later, in 1898, a mysterious scientist announced by radio that he built portals inside the Mist regions, and that portals directly leads to other portals in Mist regions on the Moon, Mars and Venus (all mysterious and inhabitable).
There is a competition for the new colonies since then.

It's a world where technology evolved differently. There are new human species caused by radiations, drugs epidemics (red rust and green rust on Mars and Venus) or experiences made possible by some stranges substances of the Mist. Biology and other technologies are in advance. On the contrary, television still doesn't exist, no more than rockets or a clear idea of a computer.