Poland

Officially, Warsaw became the capital of Poland in 1952.

An excerpt from the article 31 facts about Poland
Although it is said that Warsaw has been the capital of Poland since 1596, this is not entirely true. At that time, only the king and his court moved to Warsaw and it became the residence city of His Majesty the King. It was not until 1918 that Warsaw was declared the capital of Poland, while in 1952, the Republic Polish People constitution formally stated that Warsaw was the capital of Poland.