The Mongol invasion of Rus' can be divided into two phases. In the winter of 1237-38, they conquered the northern Rus' territories (the principalities of Ryazan and Vladimir-Suzdal) with the exception of the Novgorod Republic, but in the spring of 1238 they retreated back to the Wild Fields. The second campaign, aimed at the southern Rus' territories (the principalities of Chernigov and Kiev) came in 1239. The Sack of Chernigov was part of the Mongol invasion of Rus'.