Long ago there was one world called “earth” but the people on that planet were constantly at war, so early in its history some great power or powers (be it the Force or the gods) divided the world so the people would not fight. They or it took the people to other planets much like their homelands to live in peace, but even in these un-diverse planets people still rose against their brethren. The power or powers at this time chose not to further divide the people but to help them. With the help of the power or powers the societies began to coexist more or less in peace. Some planets that prove the exception to the division rule are Centerland planet, Aoteroa, and Donatainus. These three planets have such diversity that they are said to be experiments by the power or powers to see if people were ready to reintegrate. The answer these planets provide is a resounding maybe.
In the most recent centuries, people have begun to visit other planets through the use of Spelljamming. In a relatively short period of time many of the planets in our galaxy were now sailing through space. This was most spurred on by the tinker Gnomes and the Arcane who brought their developments to many planets. Strong undivided planets like the Galactic Empire quickly filled the air of other planets and established a strong holds on them. Those that threw off the hold of the Empire established a democracy called The Galactic Alliance for Interstellar Peace (The Alliance or G.A.I.P.). This held many planets together so as to avoid again being taken over by the Empire. Some planets found even this hold too crushing and thrust it off in favor of ruling themselves, they are called the Rebels.