From The TimeSplitters Wiki

The Mox Civil War was a sub-war of the TimeSplitter War between the several races of Mox on Planet X which lasted around 50 years with 2280 at it's peak.

Introduction

There were no apparent leaders in the conflict. The two factions, the Meezors and the Ozors fought each other to the brink of extinction. During the war, the Koozer Mox lay in wait before taking over once the two other factions had been wiped out.

The TimeSplitters

The relation between the Mox and the TimeSplitters is unclear. In the TimeSplitters 2 mission, a spaceship is discovered, having crashed into the ground inside is the Time Crystal (easy mode) and some TimeSplitters. It is possible that when hiding the Time Crystals, the TimeSplitters sent to hide the one on Planet X got shot down and crashed into the ground, just like Hank Nova.