Military action
The Xholx arrive at the Youti islands to find their new home occupied by what appear to them as aliens— and promptly begin to remove the strange inhabitants by force.
The precursors who lived upon the islands possessed incredible knowledge, but had not been to war within the untold aeons that was their history. They possessed little to no weapons as the concept was simply unimaginable to them. Most of the war was spent by the Xholx travelling from settlement to settlement, with the genocide of the ancient people taking only a modicum of the almost year-long affair.