Part of my idea came from the guy before me so show him a lot of support.
What if Charlemagne as he ran the empire realized the issue of succession with his son if he had more than one heir and two realized that an eventual uniting of the western and eastern empire can be more beneficial to Christendom. Where a line of competent rulers through the span of a few hundred and a dozen or so rulers later could conquer and unite all of Europe. Depending on how he governs it, assimilating them through a Roman, Frankish, or combination of the two plus the eastern Roman Empire like culture, he could make an Latin, Christian empire throughout all of Europe. the empire might conquered through Siberia and probably take some of the Middle East (which I mean turkey to the Caspian sea, the entire east coast of the Mediterranean which is modern day Lebanon and Israel, and maybe Mesopotamia) but after that I’m not sure. The America’s will be discovered eventually, most likely by Europe but I don’t know what will happen from there.