Russian rule there ended as a result of the advance by the armies of the Central Powers in 1915 during World War I.

Originally, the Kingdom had an area of roughly 128,500 km2 and a population of approximately 3.3 million. The new state would be one of the smallest Polish states ever, smaller than the preceding Duchy of Warsaw and much smaller than the Polish-Lithuanian Commonwealth which had a population of 10 million and an area of 1 million km2.[8] Its population reached 6.1 million by 1870 and 10 million by 1900. Most of the ethnic Poles in the Russian Empire lived in the Congress Kingdom, although some areas outside it also contained a Polish majority.

The Kingdom of Poland largely re-emerged as a result of the efforts of AdamJerzy Czartoryski,[10] a Pole who aimed to resurrect the Polish state in alliance with Russia. The Kingdom of Poland was one of the few contemporary constitutional monarchies in Europe, with the Emperor of Russia serving as the Polish King. His title as chief of Poland in Russian, was Tsar, similar to usage in the fully integrated states within the Empire (Georgia, Kazan, Siberia).

Theoretically the Polish Kingdom in its 1815 form was a semi-autonomous state in personal union with Russia through the rule of the Russian Emperor. The state possessed the Constitution of the Kingdom of Poland, one of the most liberal in 19th century Europe,[10] a Sejm (parliament) responsible to the King capable of voting laws, an independent army, currency, budget, penal code and a customs boundary separating