East Prussia was an exclave of Prussia that existed from 1919 until World War II. It was created as a result of the Treaty of Versailles at the end of World War I, when parts of the old Polish province of Royal Prussia were returned to Poland after 150 years of Partition.
East Prussia was located in the south-east corner of the Baltic Sea. It's capital was Königsberg, present day Kaliningrad. The northern part of East Prussia corresponds to today's Russian Kaliningrad Oblast, the southern parts (landscape Warmia and land of lakes Mazury) now belong to Poland (Warminsko - Mazurskie Voivodship, capital: Olsztyn(German: Allenstein).
In 1939, East Prussia had 2.49 million inhabitants. The German population was evacuated at the end of World War II under quite dramatic circumstances. Russians, Belorussians and Ukrainians were forced to settle in the northern part - Sambia, Polish refugees from former eastern parts of Poland were forced to settle in Warmia i Mazury.