Military action
Humanity, just 6 years after signing a 15-year peace deal, goes on the offensive against the Goners (3-4 foot tall lizard/velociraptor people) .
Goner remover 9000 is used by every nation to take over planets as quickly as possible before the main bulk of the Goner military, which is busy fighting the The LIR or League of Intelligent Races , can send enough of its forces back to stop humanity's progress into their territory.
By the end of it, humanity has 90% of what used to be Goner territory and the majority of the Goner species is dead. Humanity's new enemy is the LIR and the 6 Nations Period truly begins.