Well, sufficient nautical technology would certainly be a very logical prequisite. Which, if you want to be nitpicky about it, would mean the basically Mediterranean-centered factions that mainly use galleys for their seagoing needs would also have to get "roundships" at some point, as galleys and oceans simply don't mix very well. Or, rather, there's a reason galleys were only ever widely used on the small handful of relatively calm "inner seas" (like the Med) and major inland waterways (as in China) of the world.