For a long time, the history of Prussia was practically synonymous with that of the Teutonic Order. In 1227, the Teutonic Order came into the Kulmer Land (East Prussia, at the Vistula), after they had been thrown out of Transsylvania. In 1237, they united with the Livonian Brotherhood of the Sword. The OTL battle of Liegnitz (where many knights fell) never happened, so the Order hadn't to pay a high blood toll; OTOH, the stronger Russia also deterred them from attacking, so there never was an Alexander called Nevsky.