It is part of Russia.
Because the victorious Allies of World War 2 wanted it that way that Prussia is part of Poland, Russia, and Lithuania.
Kaliningrad:(part of Russia) and Lithuania
Kaliningrad
The Enclave of Kaliningrad
Kaliningrad
Kaliningrad Oblast
The Kaliningrad Oblast is a Russian exclave located between Poland and Lithuania, along the Baltic Sea. It is geographically separated from the rest of Russia, with Poland to the south and Lithuania to the north and east. Kaliningrad has a strategic significance due to its location on the Baltic coast.
Kaliningrad
The enclave of Kaliningrad
The military operation known as blitzkrieg was developed by Heinz Guderian of the German Army. Guderian lived from 1888-1954 and lead troops in Poland, France, and Russia.
In 1025, the Kingdom of Poland developed. Poland became a part of Russia in the 1700's. Poland stood on its own again in 1918.