I didn't realize Napoleon thought of going to Constantinople. Hmmm...
POD , a carriage accident kills Louis XVI and Queen Marie Antoinette in 1783. The U.S. is largely unaffected and still has its Constitution, but a decision is made that all territories would be free - that is, without salvery - as young Dauphin is influenced by regents who not only realize France is in awful shape and needs reforms but who also is anti-slavery. His views are adopted by Jefferson, who has always admired France and who takes takes and man's ideas and runs with them when in 1787 he is ambassador to France.
Napoleon goes to Constantinople, where he starts to rise in power, while reforming the Ottomans. However, he faces challenges from those who greatly distrust him. The Ottomans break into a Civil War eventually between reformers and traditionalists, while Europe's nations form into staunch alliances of France, Spain, and Austria versus Britaina nd Prussia, with German and Italian states in the middle and both sides courting Russia.
Napoleon's forces gain the upper hand, and Napoleon launches an invastion of Persia to secure its Eastern borders. He then attacks with his full military might agaisnt Russia, which had attacked thinking the Ottomans would be busy with the Persians for a lot longer. Britain is agaisnt Russia at first, fearing the Ottomans will lose (and Britain not wanting to see Russia get Constantinople). However, after some initial Russian success (since the Ottomans were busy with Persia) the British see Napoleon crushing the Russians and they begin to wonder if they made the right call. Austria, in order to gain territory, and Sweden, to see if they can get something back after the losses in the Great Northern War, join in, and the Swedes capture St. Petersburg.
Starting with a crushed Russia by 1810 would be a very interesting start.Who does Napoleon go after next? Could he try to smash Austria fromt he east to get Hungary or even Vienna?
Meanwhile, the U.S. has had skirmishes with Spain over Louisiana, but even if the rest of Europe doesn't get into this war (and they might) the Spanish had major economic problems. Eventually, Mexico woudl probably revolt and the U.S. would help in exchange for land, so would get some of Texas and the West, anyway - perhaps San Francisco Bay are but not Los Angeles.
Napoleon might see Russia, not Britain, as the #1 enemy he'd like to crush for good in this TL. But, it's so big, I wonder if he could. Others might start to turn against him. And yet, if the Ottomans are destroyed, Britain would worry about wh takes Constantinople. Unless they can inspire a Greek revolt and let a Greek kingdom be a puppet state - except OTL they only held the penninsula after their war for independence, nothing near what they do today. So, whatever the outcome there it might seem very strange as opposed to OTL.