Albert Barnes Commentary 2 Kings 9:14

"So Jehu the son of Jehoshaphat the son of Nimshi conspired against Joram. (Now Joram was keeping Ramoth-gilead, he and all Israel, because of Hazael king of Syria;" — 2 Kings 9:14 (ASV)

Had kept - Rather, this means “was keeping watch.” The city had been taken, but with the war continuing and the danger of the Syrians recovering it, Joram and all Israel (that is, the whole military force) were guarding the recent conquest while Hazael threatened it.