How did Kaliningrad, Russia's only enclave, come from?

Originally known as East Prussia, this place was the territory of Teutonic knights in the Middle Ages, and its residents were mostly Germans.

After the division of the Holy Roman Empire, East Prussia was loyal to Poland. In Bismarck's time, East Prussia returned to Germany.

After World War II, East Prussia was occupied by the Soviet Union. Before that, most residents of East Prussia had already evacuated to Germany, and they could never go back. So East Prussia completely became Soviet territory. After World War II, most of the new residents were Russians, and the Soviet government changed the place name to Kaliningrad.

After the disintegration of the Soviet Union, the three Baltic countries became independent, but Kaliningrad was not, so Kaliningrad became an enclave.