After the discovery of Istara and its Earth-like conditions, humans thought it would be best for the survival of the species if we were spread throughout the stars. This was the purpose of the First Relocation.
The population of Earth was split in half, with one half remaining on Earth while the other was moved to live on Istara.
Many people had to be forced into complying, and it was far from a popular decision. It left many people in ruins, both emotionally and physically, and families were separated.
However, despite its unpopularity among humankind, the First Relocation pales in comparison to the retribution of the Second Relocation.