I give it a try.
This happened in Europe:
Somehow Russia and France come to terms, so instead af the 1812/13 Russian debacle Napoleon can preserve his strength. Fighting in Europe continues a few more years - Napoleon finally manages to pacify Spain. (beating a British army in the process).
Wary of Russia Napoleon wants to strengthen the Duchy of Warsaw and trades Galicia for the Illyric Provinces.
In Europe the Confederation of the Rhine, Spain, Switzerland, Italy and Naples are French puppets, the (new) Polish Kingdom, Austria and Denmark are Allies (though Austria only because of dynastic ties)
Sweden, Russia and the Ottoman Empire are neutral (Russia looking to the Southeast while the OE struggles with Egypt)
Britain still supports Portugal and to a certain degree also Prussia (both Poland and Austria are considering the First Division of Prussia

)
Many Germans, Dutch and Spanish relocate to the Americans (the Spanish to Mexico and South America, thoe others to the US, where they lobby against France.
1821 Napoleon Dies
His son Napoleon Franz suceeds him (until 1832, when he dies without issue). During this time France - while it experiences some minor uprisings - has a rather peaceful time of growth. In 1827 France Britain and Russia support the Greek revolution (which serves to lower the continuing tensions between France and UK)
1832 - Charles Louis Napoleon ascends the French Throne
1837 Victoria ascends the throne, but is killed by a madman - Edward Oxford - 1840 (OTL the assassination attempt failed) - ernst August ascends the throne, but Britain is distracted as his rule is not undisputed.
1841 Napoleon III (as he styles himself) also wants to enlarge France as his predecessors. His eyes fall on Loisiana which was sold away by the great Napoleon. The constant lobbying by German and Dutch and the Attack on the French ambassador in Washington by a Dutch emigree are the perfect excuse to open hostilities. (Cuba and Puerto Rico are nominally Spanish posessions but serve as bases for an attack). Mexico is persuaded by France to join in - the price is Tejas returned and French money.
on June 22nd 1841 French Troops land in New Orleans, Mobile and Charleston. A Mixed Mexican/French corps marches over the Mexican/Texan border. The French Fleet bombards Boston.