Based on a suggestion by Herbert James Paton, it was first proposed in 1919 by Lord Curzon, the British Foreign Secretary, to the Supreme War Council as a diplomatic basis for a future border agreement.

[1][2][3] The line became a major geopolitical factor during World War II, when the USSR invaded eastern Poland, resulting in the split of Poland's territory between the USSR and Nazi Germany roughly along the Curzon Line in accordance with final rounds of secret negotiations surrounding the Molotov-Ribbentrop Pact.

After the German attack on the Soviet Union in 1941, Operation Barbarossa, the Allies did not agree that Poland's future eastern border should be changed from the pre-war status quo in 1939 until the Tehran Conference.

The Allied arrangement involved compensation for this loss via the incorporation of formerly German areas (the so-called Recovered Territories) into Poland.

At the end of World War I, the Second Polish Republic reclaimed its sovereignty following the disintegration of the occupying forces of three neighbouring empires.

The Allied victors agreed that an independent Polish state should be recreated from territories previously part of the Russian, the Austro-Hungarian and the German empires, after 123 years of upheavals and military partitions by them.

[6] The Supreme War Council tasked the Commission on Polish Affairs with recommending Poland's eastern border, based on spoken language majority, which became later known as the Curzon Line.

The US President Woodrow Wilson's Fourteen Points included the statement "An independent Polish state should be erected which should include the territories inhabited by indisputably Polish populations, which should be assured a free and secure access to the sea..." Article 87 of the Versailles Treaty stipulated that "The boundaries of Poland not laid down in the present Treaty will be subsequently determined by the Principal Allied and Associated Powers."

In accordance with these declarations, the Supreme War Council tasked the Commission on Polish Affairs with proposing Poland's eastern boundaries in lands that were inhabited by a mixed population of Poles, Lithuanians, Ukrainians and Belarusians.

Following a strong Soviet counteroffensive, Prime Minister Władysław Grabski sought Allied assistance in July.

[17] The July 1920 note specifically addressed the Polish-Lithuanian dispute by mentioning a line running from Grodno to Vilnius (Wilno) and thence north to Daugavpils, Latvia (Dynaburg).

Georgy Chicherin, representing the Soviets, commented on the delayed interest of the British for a peace treaty between Russia and Poland.

During the first quarter of the 20th century, a representative of the first political group was Roman Dmowski, an adherent of the pan-slavistic movement and author of several political books and publications[24] of some importance, who approached the issue pragmatically, but advocating for incorporation of available land based on a ethnographic principle combined with a theory of easy assimilation of Belarusians within a centralised Polish state- the task potentially to be shared with Russia concerning Belarusians beyond the border which he viewed it would be possible to incorporate and assimilate.

This resulted in a modification of the Dmowski Line in negotiations for the Treaty of Riga, in which the Polish delegation (consisting of a majority of parliamentary representatives, Dmowski’s Zjednoczenie Ludowo-Narodowe being the strongest party) unilaterally ceding claims to the Minsk area without basis on the line of actual control, and despite it having a higher Polish-identified population (in absolute and proportionally) than many of the areas still claimed within the border.

An anti-communist, but believing in the inevitability of a White victory in the Russian Civil War he wished to concentrate on resisting a more dangerous enemy of the Polish nation than Russia, which in his view was Germany.

The most powerful representative of the opposed group was Józef Piłsudski, a former socialist who was born in the Vilna Governorate annexed during the 1795 Third Partition of Poland by the Russian Empire, whose political vision was essentially a far-reaching restoration of the borders of the Polish–Lithuanian Commonwealth, ideally in the form of a multinational federation.

In September, after the military defeat of Poland, the Soviet Union annexed all territories east of the Curzon Line plus Białystok and Eastern Galicia.

When the Soviet Union ceased to exist in 1991, the Curzon Line became Poland's eastern border with Lithuania, Belarus and Ukraine.

Poles constituted majorities in the main cities (followed by Jews) and in some rural areas, such as Vilnius region or Wilno Voivodeship.

After 1945, the Polish population of the area east of the new Soviet-Polish border was in general confronted with the alternative either to accept a different citizenship or to emigrate.

Polish population east of the Curzon Line before World War II can be estimated by adding together figures for Former Eastern Poland and for pre-1939 Soviet Union: