The Suwałki Agreement established a ceasefire line between Poland and Lithuania but was violated within days, triggering Polish seizure of Vilnius and decades of Polish-Lithuanian hostility.
Key Facts
- Date signed
- October 7, 1920
- Registered with League of Nations
- January 19, 1922
- Vilnius occupied by Żeligowski
- October 9, 1920
- Agreement effective time
- Noon, October 10, 1920
- Central Lithuania incorporated into Poland
- 1923
- Polish administration of Vilnius Region ended
- Autumn 1939
By the Numbers
Location
Cause → Event → Consequence
Following World War I, both Poland and Lithuania re-established independence but lacked defined borders, leading to armed conflict over the Suwałki and Vilnius Regions. After Polish forces defeated Soviet troops at the Battle of the Niemen River in late September 1920, Piłsudski began planning a covert seizure of Vilnius. League of Nations pressure compelled Poland to negotiate, though Polish leadership intended the talks to mask the forthcoming operation.
On October 7, 1920, Poland and Lithuania signed the Suwałki Agreement, establishing a ceasefire and a demarcation line through the disputed Suwałki Region extending to the Bastuny railway station. The line did not explicitly address Vilnius or its surrounding area, leaving Lithuania's most prized territorial claim unprotected by the accord's terms.
Within days of signing, Poland broke the agreement when General Lucjan Żeligowski, acting on Piłsudski's secret orders, staged a feigned mutiny and occupied Vilnius on October 9, before the ceasefire took effect. He established the Republic of Central Lithuania, which was incorporated into Poland in 1923. The episode poisoned Polish-Lithuanian relations and left Lithuania without diplomatic ties to Poland until 1938.
Political Outcome
Ceasefire and demarcation line established, but violated by Poland; Vilnius seized and incorporated into Second Polish Republic by 1923.
Contested Suwałki and Vilnius Regions with active Polish-Lithuanian hostilities
Poland in de facto control of Vilnius Region; Lithuania in formal non-recognition of Polish authority over Vilnius