What if both Byzantine and Sassanid Empires became established gunpowder empires by late 5th century?
Ok, so this might be far fetched, but what if gunpowder was discovered in China during the Three Kingdom periods, and from there it spread to west. And while the Western Roman Empire still collapsed, Eastern Roman Empire managed to fully utilize rudimentary gunpowder weaponry alongside with Sassanid Empire by late 5th century. How might the history have changed? How long would both empires manage to keep the secret of gunpowder weaponry from their neighbors? Would it give competitive edge for them against the nomadic groups/empires that would threaten them throughout centuries like the remaining Huns, Avars, Arabs etc.