Cataclysm of Iron
The battles took place in the "Belt of Iron", a region of Segmentum Tempestus and Segmentum Pacificus home to numerous lesser Forge Worlds. Many of these worlds declared for the Dark Mechanicum upon the outbreak of the Schism of Mars. Sporadic fighting between loyalist and traitor Mechanicum elements in this region erupted into full-scale war in 010.M31, pitching the traitor Forge Worlds of Incunabula, Urdesh, Valia-Maximal, and Kalibrax against the loyalist worlds of Graia, Arl'yeth, and Atar-Median. The worlds of Arachnis and Jerulas Station meanwhile both fell into their own civil wars. In the subsequent devastating fighting, many nearby worlds were swallowed up in the destruction.