Thinking Medieval With a Twist: It's a small world...sort of

Ancient Rome and Ancient China were the biggest powers of their day on Earth. They didn't exchange ambassadors or anything that formal like that, but they traded with people who traded with people who traded with people who had traveled to the other empire. They had at least heard of each other.   Marco Polo completed his famous journey to the Orient and back was between 1271 and 1295. Magellan's famous voyage around the world was in 1519.   Like most preindustrial Earth people, most Scarterrans do not travel very far from the place of their birth giving them a complex relationship with strangers, but Scarterra does have a few allegorical equivalents to Marco Polo or Ferdinand Magellan. More than a few actually. As a result, Scarterrans have a bit better of an idea of what faraway lands are like, at least in the educated upper classes.   That doesn't mean that the people East Colassia and West Colassia have an active trading relationship or warm relationship, but they have enough regular contact that they know the basics of the politics and culture of the other continent.   This is because of a number of reasons.  

Scarterra is physically smaller than Earth

  I'm still working on the specific measurements, but I am operating on the working assumption that Scatrterra has roughly half of the surface area of Earth.   Since the world is smaller, reason stands that it takes less time and effort to circumnavigate the globe. Scarterra isn't technically a globe, it's a bulging cylinder, but you can still circumnavigate it east-west, just not north-south, the Void gets in the way, but in historical Earth, no one was circumnavigating the Earth north-south until well after the Industrial Revolution.  

Scarterra's sea lanes are a bit more sailor-friendly than Earth's

  Scarterra as a whole is roughly oriented like the Mediteranean Sea on Earth. A lot of land is clustered around a central body of water and this lets a sailor chart a course where they can sail long distances without going too far from the coast, so they can make landfall for supplies often.   And at the very center of the world is Mera's Lake which is a limitless source of fresh water that sailors can stock up on.  

About 1% of Scarterra's population has some limited kind of supernatural power

  About 1% of the population are theurgists, mages, or spirit loas. Not all of these abilities apply to travel, but some of them do.   Magic can help navigation, create drinkable water, predict the weather, find true North, and do other varied effects that a clever captain can use to make surviving long journeys easier.  

There are fewer language barriers

  Relative to historical or contemporary Earth, there are fewer different languages spoken across Scarterra so it is easier to find common languages with foreign people making travel and trade easier and safer.   No magic is truly common in Scarterra, but magical translation magic is more common than most.  

Here there be Monsters!

  Scarterra has dangerous creatures and supernatural anomalies, too many to mention them all individually. This makes long-distance more difficult. While Scarterra has several allegorical Marco Pollos and Ferdinand Magellans, it also has more than its fair share of Amelia Earharts that disappear en route.   That said, these supernatural threats do not completely negate the factors above. Long distance travel on Scarterra is not especially fast, easy, or safe but it is far from impossible.