The Grekins campaign was the name of the series of battles fought by Admiral Erk Grekins, and the New Republic forces opposing him. It spanned over several months, from late 13 ABY to 14 ABY. Most of the battles took place in the Clantosh system, and were collectively referred to as the Clantosh campaign.
Decades before the formation of the Grekins Hierarchical Empire, there was a Battle of the Clantosh system during the Clone Wars. However, that was considered a single, system-wide battle, rather than the long campaign between Grekins and the New Republic.