What if the Roman Empire never fell to invaders, instead conquering and pacifying the local Germanic tribes, slowly expanding to encompass all of Europe?
Rome Expanded until roughly 1200 AD when it met the Reborn Chinese Empire. The Reborn Chinese Empire had been conquering Japan, Korea, and Vietnam, which gave it the strength required to push back the Mongolian invaders. In 1500, the Chinese then counter-invaded the Mongol lands, deposed of Genghis Khan and established their own emperor as that of the Mongol Horde. Following the technology boom of the 17th Century, the warring Rome and China began experiencing rebellions throughout their empires, as a result of the constant warfare plaguing the two nations. As such, the Roman and Chinese Royal Families intermarried, forming the Grand Earth Empire, in order to stop the rebels. By 2011, the Grand Earth Empire had suffered countless losses at the hands of the rebels, and is now a dwindling polity in the Italian Peninsula and East Asia.
Roman Defeat of the Germanic Invaders
By the time of the Great Migration, the Roman Army had shrunk considerably. However this was by no means the end of the Empire, as Furious Luscious, a Roman not present in OTL, led the Romans to victory against the Germanic tribes, incorporated their lands into the Empire, and was later named Emperor.