The Mongols defeat the Volga Bulgars in 1236, and in December 1237 Subutai and Batu lead an army of six hundred thousand across the frozen Volga River.

The Mongols spread destruction and death through Russia.

Moscow, Vladimir, and other northern Russian principalities are destroyed before summer 1238.

Subutai now turns south to the steppe region around the Don, to allow his army to rest, to regain strength, and to prepare for new advances.

Apparently his timetable is delayed for a year by a dispute between Batu and other royal princes commanding various hordes.

Nonetheless, this additional time gives Subutai an opportunity to accumulate still further information about central and western Europe from his spies.