To the west of Moscow and east of Latvia and Estonia was the Novgorod Republic. Novgorod was ruled by a Prince who was appointed or elected by a strong city council, rather than inheriting the role automatically at birth. The Republic was a stable medieval state with trade contacts all through Europe (the archbishop asked church fees to be paid in bolts of wool cloth from Flanders!). Traders on the Volga and Dniepr rivers passed through Novgorod, whose rulers had also intermarried with Swedish kings in the past.
Novgorod spoke a Slavic language, but it’s anachronistic to refer to its region as “Russia” at this time. Instead, there were principalities linked loosely by similar language and culture. The area around Moscow was ruled by the Prince of Vladimir-Suzdal, and Moscow itself was just a town. Novgorod controlled territory from the Volga River to the Baltic Sea.
When the land to the south was ruled by the Golden Horde, Novgorod chose to become a tribute-paying vassal of the Mongols in Sarai. It had become plain that not paying tribute was a very poor choice. All of the cities in its Russian neighbor-network had been burnt and depopulated.
In the 12th century just past, Sweden and Novgorod had many frontier battles over ports and trading posts on the Baltic and around Finland. The German-based Hanseatic League saw Novgorod as a trade rival. Further, Sweden no longer looked on the Eastern Orthodox city as Christian, as its ties to Rome grew stronger.
Because Novgorod’s network had been weakened a lot by the Mongols, the Teutonic Knights, representing Swedish and German interests, chose to invade. They occupied several Novgorodian cities along Lake Peipus, the large lake along the border of Estonia. Novgorod had to act, so the Republic called back its strongest leader from exile.
Aleksandr Nevsky was the grandson of a Rus prince with strong Byzantine ties representing both Kyiv and Vladimir-Suzdal, the strongest princedom of the region. Their family brought some of the grandeur of Constantinople into the Russian forests, building the wooden onion-dome churches that we still see today. Aleksandr had served as the Prince of Novgorod already (and been banished) by the time he was 20. In 1241, the city decided they needed him to defend against the Teutonic knights.
Nevsky chose to fight on the frozen lake itself. In April, the lake was still frozen so solid that it could support thousands of men fighting on its surface! That’s a cold climate! During the battle, the Teutonic knights (with Estonians they had pressed into service) fought for two hours but began to find the icy surface getting slick. Nevsky chose to bring a reserve force onto the lake at that time. Some legends say that the ice broke up and the Teutonic knights fell into the water, but this may have been Sergei Eisenstein’s cinematographic invention in 1938. In any case, Nevsky won and the Teutonic knights did not choose to try Novgorod’s territory again.
Nevsky’s attitude toward the Mongols was that they were the best choice of masters on offer. He became their regional tax-enforcer, not just unwillingly an ally but openly a friend and supporter. The Mongol Khan supported him in becoming Grand Prince of both Kyiv and Vladimir, and he actively helped defend their rule against invaders. He saw Rome and its allies as a greater threat to his land than the Mongols, who merely wanted tribute. So in one of the weirder twists of this period, Christian Novgorod was saved from Christian Germans so that it could serve the Mongols.