sentences:  The First Prussian Uprising was influenced by three major events.Firstly, the Livonian Knights - a subsidiary of the Teutonic Knights - lost the Battle of the Ice on Lake Peipus to Alexander Nevsky in April 1242.Secondly, southern Poland was devastated by a Mongol invasion in 1241; Poland lost the Battle of Legnica and the Teutonic Knights lost one of its most trusted allies that often supplied troops.