There are 6 regions in Pokemon, each one introduced in a new generation of games. In the second generation, I remember being able to travel to the first region, but other than that, that is the only connection I know between the regions.
Now, I know each of theses regions have representations in the real world (mostly based on Japan, though Gen VI is based on France, I believe), but what about in game? Is there any connections between the regions other than the first two? And is there any explanations given about the other regions? Or does each successive generation introduce new Pokemon, and a new region, and completely ignore that the previous region existed?