My guilty pleasure when worldbuilding is creating varied and unique cultures, however, different cultures are often the result of distance between each other (which allows them to develop unique customs and stuff). For the sake of my story I'm hoping these different countries can be closer together, meaning I have to find new barriers between them besides distance. Could mountains work? Maybe a long deep canyon? Perhaps they are all island countries?
For background, the time period is late medieval/early renaissance period, however each culture is kind of at their own pace and some may be more advanced than others. At the time in which my story takes place, all of these cultures have just gotten to formally know each other (maybe within the last 50~100 years?) and have become more connected, which means trading, new ideas, possibly conflict, idk.