Curzon Line

The Curzon Line was put forward by the Allied Supreme Council after World War I as a demarcation line between the Second Polish Republic and Bolshevik Russia and was supposed to serve as the basis for a future border. In the wake of World War I, which catalysed the Russian Revolution of 1917, the Russian Empire disintegrated in the ensuing Russian Civil War. Several countries, including Poland, used this occasion to declare their independence. Hostilities erupted when Polish and Bolshevik troops, approaching from opposing directions while taking over the territories of Ober Ost from the retreating German troops, met in the city of Masty.

The Allied Supreme Council tasked the Commission on Polish Affairs with recommending Polish eastern borders. The Allies forwarded it as an armistice line several times during the war, most notably in a note from the British government to the Soviets signed by Foreign Secretary Lord Curzon of Kedleston. Both parties disregarded the line when the military situation lay in their favour, and it did not play a role in establishing the Polish-Soviet border in 1921. Instead, the final Peace of Riga (or Treaty of Riga) provided Poland with almost 135,000 square kilometres (52,000 sq mi) of land that was, on average, about 250 kilometres (160 mi) east of the Curzon line.

With minor variations, the Curzon line lay approximately along the border which was established between the Prussian Kingdom and the Russian Empire in 1797, after the third partition of Poland, which was the last border recognised by the United Kingdom. Along most of its length, the line followed an ethnic boundary - areas west of the line contained an overall Polish majority while areas to its east were inhabited by Ukrainians, Belarusians, Poles, Jews, and Lithuanians. Its 1920 northern extension into Lithuania divided the area disputed between Poland and Lithuania. There were two versions of the southern portion of the line: "A" and "B". Version "B" allocated Lviv to Poland.

The line was a geopolitical factor during World War II, when Joseph Stalin successfully pressed for its use as a Polish-Soviet border. Throughout the war until the Teheran Conference, the British Government did not agree that Poland's future eastern border should be moved west to the Curzon Line; but Churchill's position changed after the Soviet victory at the Battle of Kursk. Following a private agreement at the Tehran Conference, confirmed at the 1945 Yalta Conference, the Allied leaders Franklin Roosevelt, Winston Churchill, and Stalin issued a statement affirming the use of the Curzon Line, with some five-to-eight kilometre variations, as the eastern border between Poland and the Soviet Union. When Churchill proposed to add parts of East Galicia, including the city of Lviv, to Poland's territory (following Line B), Stalin argued that the Soviet Union could not demand less territory for itself than the British Government had reconfirmed previously several times. The Allied arrangement involved compensation for this loss via the incorporation of formerly German-held areas (the Recovered Territories) into Poland. As a result the current border between the countries of Belarus, Ukraine and Poland is an approximation of the Curzon Line.