The first extraterrestrial world humanity set their eyes on. Finding Jusaw was a struggle, and getting there a hell of a lot worse, but it seems suitable for human habitation.
It was not suitable for human habitation.
As with any first try, the first attempt to colonize Jusaw was woefully underplanned. Ill-equipped, the colonists all went MIA presumed-KIA.
As the first world attempted to put together a crew that would survive, it gave the space agencies of underdeveloped nations time to play catch-up. So, when the first successful colonists arrived on Jusaw, they were quickly followed by competitors and competitors.
When humans brought the equipment and knowhow to survive, they also brought war.