The lake district was shaped by the Pleistocene ice age. Many of its hills
are parts of moraines and many of its lakes are moraine-dammed lakes. From 13th
century on, the Lakeland was successively part of the monastic state of the
Teutonic Knights, the Duchy of Prussia, and the Prussian province of East
Prussia. In modern times, while part of the German Empire, it was the location
of the First Battle of the Masurian Lakes (1914) and the Second Battle of the
Masurian Lakes (1915) during World War I. At the end of World War II (1945),
following the decision taken at the Potsdam Agreement, all national borders
were redrawn
