Curzon Line , the basis for the eastern boundary of Poland. It was first suggested in 1919 at the Versailles Peace Conference by Lord Curzon of Great Britain, who hoped to settle a long-standing border dispute between Russia and Poland. Curzon's proposal would have given Poland most of those areas inhabited by Polish majorities, but it did not recognize Poland's claims to territory populated by Russians.

Dissatisfied, Poland seized Vilna, capital of Lithuania, and attacked Russia (1920). Poland and Russia finally agreed, under the Treaty of Riga (1921), to put the border about 100 miles (160 km) east of the Curzon Line. At the Yalta and Potsdam conferences (1945), Great Britain, the Soviet Union, and the United States reversed this arrangement. The Curzon Line, with small deviations, became the eastern boundary of Poland. In return for land given to the Soviet Union, Poland received German territory to the west.