While the vast panoply of Great Houses and their attendant populaces are dispersed throughout the Known Universe, there are two places in the Imperium one can be certain they gather: Corrinth City, the Imperial Seat on Kaitain, and the desert planet Arrakis, the only place where the spice-drug mélange can be found.
Arrakis, in particular, draws representatives from all the Great Houses, hoping to improve their standing in the Landsraad. As the ongoing War of Assassins between House Atreides and House Harkonnen drags into its tenth year, any definitive resolution is still very much in doubt.
The various Great Houses and their envoys are eager to engage in the conflict, either by openly taking sides or by acting covertly. They believe that once the struggle is resolved, a new power dynamic will emerge, placing those who supported the winning side in a dominant position.