Operation False Horizon was an offensive that was launched by the Cularin Militia during the time of the Clone Wars, to try and drive the Thaereian military out of the Cularin system. The Militia captured or besieged all of the Thaereian bases in the system, causing most of the Thaereian troops on the planet Cularin to withdraw to the platform city Soboll.
Sources
False Horizon on Wizards.com (original site is defunct) (First mentioned)
Destabilization on Wizards.com (original site is defunct)- Yara: The Unauthorized Biography on Wizards.com (original site is defunct)