The Sejny Uprising or Seinai Revolt (Polish: Powstanie sejneńskie, Lithuanian: Seinų sukilimas) refers to a Polish uprising against the Lithuanian authorities in August 1919 in the ethnically mixed area surrounding the town of Sejny (Lithuanian: Seinai). When German forces, which occupied the territory during World War I, retreated from the area in May 1919, they turned over administration to the Lithuanians. Trying to prevent an armed conflict between Poland and Lithuania, the Entente drew a demarcation line, known as the Foch Line. The line assigned much of the disputed Suwałki (Suvalkai) Region to Poland and required the Lithuanian Army to retreat. While the Lithuanians retreated from some areas, they refused to leave Sejny. Polish irregular forces began the uprising on August 23, 1919,