Nowadays distance between countries doesn't matter too much. One of the United State's worst enemies is on the other side of the world! There have been wars that are fought thousands of miles away from the borders of countries it affects. But in medieval and ancient times, there were no planes or fast methods of transportation.
But how far apart exactly can two countries be in an ancient world? Pretend that there are no oceans and the world goes on forever. If two countries were once the same people, at what point would communication be impossible? If there somehow was a very, very large gap between these countries, what methods could these countries use to at least stay conscious of each other over long periods of time? Remember, this is theoretical and is not about Earth.
(Edit: These countries only have horses as the fastest method of transportation. This other world has a climate like Middle-Earth in the fact that it has the same relative temperature but the biomes, landforms, and most things vary. Ancient means about 2,000 years ago. Remember that this question is about the maximum number, because I mean like the distance can be much bigger than Earth itself.)