The origin of the War was that Cetaganda wanted to expand its control of the regions around it, and the Hegen Hub was a useful Nexus crossroads to aim for. They stirred up the planetary governments that neighbored the hub, causing them to become extremely suspicious of each other and to build up military resources in the hub. This led in particular to Vervain, the planet that connected the Cetagandan Empire to the hub, to move much of its forces into it and to hire a mercenary force for protection, Randall's Rangers.
The Cetagandans made a deal with the new leader of Randall's Rangers, Commander Cavilo, to sell out secretly in their favor. This plot fell apart when Miles Vorkosigan and Gregor Vorbarra entered the fray.
The Vervainis made a good number of holovid dramas about the war, and Miles Vorkosigan's role in it.