page_title: Sejny Uprising
section_title: Demarcation lines
hierarchical_section_title: Sejny Uprising / Demarcation lines
context_page_description: The Sejny Uprising or Seinai Revolt refers to a Polish uprising against the Lithuanian authorities in August 1919 in the ethnically mixed area surrounding the town of Sejny. 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 Region to Poland and required the Lithuanian Army to retreat. While the Lithuanians retreated from some areas, they refused to leave Sejny, because of its major Lithuanian population. Polish irregular forces began the uprising on August 23, 1919, and soon received support from the regular Polish Army. After several military skirmishes, Polish forces secured Sejny and the Lithuanians retreated behind the Foch Line.
  The uprising did not solve the larger border conflict between Poland and Lithuania over the ethnically mixed Suwałki Region. Both sides complained about each other's repressive measures.
context_section_description: In the aftermath of World War I, the Conference of Ambassadors drew the first demarcation line between Poland and Lithuania on June 18, 1919. The line satisfied no one, and Polish troops continued to advance deeper into the Lithuanian-controlled territory. These attacks coincided with the signing of the Treaty of Versailles on June 28, which eliminated any danger from Germany. Attempting to halt further hostilities, Marshal of France Ferdinand Foch proposed a new line, known as the Foch Line, on July 18, 1919.
  The Foch Line was negotiated with the Polish war mission, led by General Tadeusz Jordan-Rozwadowski in Paris, while Lithuanian representatives were not invited. The Foch Line had two major modifications compared to the June 18 line: first, the entire line was moved west to give extra protection to the strategic Warsaw – Saint Petersburg Railway and second, the Suwałki Region, including the towns of Sejny, Suwałki, Puńsk, was assigned to Poland. Despite assurances at the time that the line was just a temporary measure to normalize the situation before full negotiations could take place, the southern Foch Line is the present-day Lithuania–Poland border.
  On July 26, the Foch Line was accepted by the Conference of Ambassadors as the provisional border between the two states. Lithuanians were not informed about this decision until August 3. Neither country was satisfied: both Lithuanian and Polish forces would have to retreat from the Suwałki and Vilnius regions, respectively. Those Germans still present in the region also objected to the boundary of the line. The Lithuanian forces (about 350 strong) left the town of Suwałki by August 7, but stopped in Sejny and formed a line at the Czarna Hańcza river – Wigry Lake, thus effectively violating the demarcation line. Lithuanians believed that the Foch Line was not the final decision, and that they had the duty to protect Lithuanian outposts in the region.
caption: Selected lines of demarcation between Lithuania and Poland in 1919–1939. Light green denotes the first line, drawn on June 18, 1919. The second, dark green line known as Foch Line, was drawn on July 27.