This alternate timeline is set in a world where the Louisiana Purchase was never completed, France never invaded Russia, won the Peninsula War, and never re-instated slavery during Napoleon´s reign. Because Napoleon's France never broke up, he was able to conquer all of Europe and be the leader of a world power over 50 years.
The main POD in this timeline is the year of 1812, when Napoleon I, after winning the Peninsula War doesn't invade Russia but instead sends troops to America. There, he declares New Spain, Cuba, and other Spanish Caribbean colonies to be under French rule.
The colony of New Spain (Mexico) didn't achieve its independence in 1821, after a long war and during an economic crisis in Spain. Napoleon's troops took over Mexico Louisiana and aided the Quebec independence movement.
After Mexico finally achieved it's independence in 1863, it did so as the most powerful of all French colonies and as a military and economic powerhouse instead of a poor and war-torn country like in real life.
The United States faced trouble right after its independence because it was completely surrounded by Britain (which still held a grudge) and Imperialist France. They didn't become a "power" right away but instead very slowly consolidated itself and became a power. After WWI the USA was one of the world's superpowers along with Mexico and Russia.
France became even more powerful under Napoleon I because instead of attacking Russia, it sent troops to the Spanish colonies after winning the Peninsula War. With almost half of North America under their control, the French gained access to more resources and manpower, enabling it to become the dominant power in Europe and even rule over all of it for a time.
Russia refused to sell Alaska to the USA or Canada and was one of the few trading partners the French Empire had. Because of this, the Russia Empire became slightly more technologically advanced than in real life and proceeded to become a superpower later on. The refusal to sell Alaska allowed them to get more money from fur trading and other arctic economies, later on the discovery of vast oil reserves aided the Russian economy and incremented its power.
The United Kingdom of Great Britain faced invasion many times while France was under Napoleon, all of those times it managed to fight the French Navy to a stalemate and repel any attempt to invade. But things did not go so well for Britain, their small island was permanently blockaded by the French Navy and goods from its colonies rarely made it through. Instead, Britain had to be able to sustain its relatively large population by itself, so after half the population were starving, the UK started growing their own food and making their own goods. They became a powerhouse of an economy because it depended on no one. By the late 1800´s, the UK was once again a proud nation and a powerful country.
The rest of the European countries were conquered and lived under the French Empire for approximately 60 years until many of them reveled. The only country that didn't suffer the Napoleonic invasion was Russia.
Other minor POD's are:
Louisiana purchase was never completed.
Quebec became independent from England and joined Louisiana as French colony.
Russia never sold Alaska.