text: sejny uprising the sejny uprising or revolt ( polish : , lithuanian : ) refers to a polish uprising against the lithuanian authorities in august 1919 in the ethnically mixed area surrounding the town of sejny ( lithuanian : ) . 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 , and soon received support from the regular polish army . after several military skirmishes , polish forces secured sejny and 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 . the conflict intensified in 1920 , causing military skirmishes of the polish – lithuanian war . sejny changed hands frequently until the suwałki agreement of october 1920 , which left sejny on the polish side . the uprising undermined the plans of polish leader józef piłsudski , who was planning a coup d 'état in lithuania to replace the lithuanian government with a pro - polish cabinet , that would agree to a union with poland ( the proposed międzymorze federation ) . because the sejny uprising had prompted the lithuanian intelligence to intensify its investigations of polish activities in lithuania , they discovered plans for the coup and prevented it , arresting polish sympathizers . these hostilities in sejny further strained the polish – lithuanian relations . eventually , poland and lithuania reached an agreement on a new border that left sejny on the polish side of the border . the polish – lithuanian border in the suwałki region has remained the same since then ( with the exception of the world war ii period ) . background during the ages , the lands surrounding the town of suwałki had been variously part of lithuanian , polish , and german borderlands . since 1569 , during the era of the polish – lithuanian commonwealth , the territory belonged to the podlaskie voivodeship and was part of the kingdom of poland rather than the grand duchy of lithuania . however , sejny was a property of dominican friars from vilnius . during the 19th century the town was part of russian - controlled congress poland . during world war i the region was captured by the german empire , which intended to incorporate the area into its province of east prussia . after the german defeat , the victorious entente was willing to assign the territory to either the newly independent poland or lithuania . the future of the region was discussed at the paris peace conference in january 1919 . the germans , whose former ober - ost administration was preparing to evacuate , initially supported leaving the area to a polish administration . however , as poland was becoming an ally of france , german support gradually shifted towards lithuania . in july 1919 , when the german troops began their slow retreat from the area , they delegated the administration to local lithuanian authorities . lithuanian officers and troops , who first arrived in the region in may , began to organize military units in the pre - war sejny county . according to russian statistics of 1889 , there were 57 . 8 % lithuanians , 19 . 1 % poles , and 3 . 5 % belarusians in the suwałki governorate . it is generally agreed that lithuanians formed the majority population in the northern suwałki governorate , while poles were concentrated in south . but , lithuanian and polish historians and political scientists continued to disagree over the location of the line that separated the lithuanian from the polish majorities . lithuanians claimed that sejny and the surrounding area were inhabited primarily by lithuanians , while the poles claimed exactly the opposite . the german census of 1916 showed that 51 % of sejny population was lithuanian . demarcation lines in the closing days 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 , , 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 has been regarded since then as the border between lithuania and poland . 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 river – lake . lithuanians believed that the foch line was not the final decision , and that they had the duty to protect lithuanian outposts in the region . uprising preparations on august 12 , 1919 , two days after the germans retreated from sejny , a polish meeting in the town attracted over 100 delegates from neighboring polish communities ; the meeting passed a resolution that " only securing the area by polish army can solve the problem . " the sejny branch of the polish military organization ( pmo ) , led by polish regular army officers adam rudnicki and wacław zawadzki , began preparing for the uprising on august 16 . pmo members and local militia volunteers numbered some 900 or 1 , 200 men ( sources vary ) . the uprising was scheduled for the night of august 22 to 23 , 1919 . the date was chosen to coincide with the withdrawal of german troops from the town of suwałki . the poles hoped to capture the territory up to the foch line and advance further to take control of the towns of , lazdijai , kapčiamiestis as far as . according to the polish historian tadeusz mańczuk , piłsudski – who was planning a coup d 'état in kaunas – discouraged the local pmo activists from carrying out the sejny uprising . piłsudski reasoned that any hostilities could leave lithuanians even more opposed to the proposed union with poland ( see międzymorze ) . the local pmo disregarded his recommendations and launched the uprising . while locally successful , it led to the failure of the nationwide coup . on august 17 , a lithuanian counter - demonstration was staged . its participants read aloud a recently issued recruiting proclamation of the lithuanian volunteer army : " citizens ! our nation is in danger ! to arms ! we shall leave not a single occupant on our lands ! " on august 20 , prime minister of lithuania mykolas sleževičius visited sejny and called on lithuanians to defend their lands " to the end , however they can , with axes , pitchforks and scythes " . according to lesčius , at the time the lithuanian command in sejny had only 260 infantry and 70 cavalry personnel , stretched along the long line of defense . there were only 10 lithuanian guards and 20 clerical staff in the town itself . mańczuk and note that the polish insurgents estimated the lithuanian forces at 1 , 200 infantry ( mańczuk also adds an estimate of 120 cavalry ) , including a 400 - strong garrison in sejny . military skirmishes according to lithuanian historian lesčius , the first polish assault of about 300 pmo members on august 22 was repelled , but the next day lithuanians were forced to retreat towards lazdijai . over 100 lithuanians were imprisoned in sejny when their commander sided with the poles . the polish insurgents also attacked lazdijai and kapčiamiestis , towns on the lithuanian side of the foch line . in early morning of august 25 , lithuanians counterattacked and recaptured sejny . polish sources claim that lithuanians there were aided by a company of germans volunteers , but lithuanian sources assert that it was an excuse used by rudnicki to explain his defeat . the lithuanian forces recovered some important documents and property , freed lithuanian prisoners and , according to mańczuk , executed several of the pmo fighters they found wounded . on the evening of august 25 , the first regular unit ( 41st infantry regiment ) of the polish army received an order to advance towards sejny . the lithuanian forces retreated on the same day when they learned about approaching polish reinforcements . according to mańczuk , they based their retreat on an erroneous report about a " large polish cavalry unit " operating to their rear ; only small groups of polish partisans operated there . later the next day , during the afternoon of august 26 , the pmo forces in sejny were joined by the 41st infantry regiment . on august 26 , a large anti - polish protest took place in lazdijai , with cries to march on sejny . the last lithuanian attempt to retake the town was made on august 28 . the lithuanians ( about 650 men ) were defeated by the combined forces of the polish army ( 800 men ) and pmo volunteers ( 500 men ) . on august 27 , the poles officially demanded that lithuanians retreat behind the foch line . on september 1 , rudnicki announced incorporation of pmo volunteers into the 41st infantry regiment . during the negotiations on september 5 , representatives of the two groups agreed to settle on a detailed demarcation line ; lithuanians agreed to retreat by september 7 . the polish regular army units did not cross the foch line , and refused to aid the pmo insurgents still operating on the lithuanian side . polish sources give total polish casualties for the sejny uprising as 37 killed in action and 70 wounded . aftermath after the uprising , poland repressed lithuanian cultural life in sejny . lithuanian schools in sejny ( which had some 300 pupils ) and surrounding villages were closed . the local lithuanian clergy were evicted , and the sejny priest seminary relocated . according to lithuanians , the repressions were even more far - reaching , including a ban on public use of the lithuanian language and the closing of lithuanian organizations , which had a total of 1 , 300 members . the new york times , reporting on renewed hostilities a year later , described the 1919 sejny events as a violent occupation by the poles , in which the lithuanian inhabitants , teachers , and religious ministers were maltreated and expelled . polish historian notes that both sides mistreated the civilian population and exaggerated reports to gain internal and foreign support . the uprising contributed to the deterioration of the polish – lithuanian relations and further discouraged the lithuanians from joining piłsudski 's proposed międzymorze federation . the sejny uprising doomed the polish plan to overthrow the lithuanian government in a coup d 'état . after the uprising , the lithuanian police and intelligence intensified their investigation of polish sympathizers and soon uncovered the planned coup . they made mass arrests of polish activists from august 27 to the end of september 1919 . during the investigations , lists of pmo supporters were found ; law enforcement completely suppressed the organisation in lithuania , arresting members . hostilities over the suwałki region resumed in summer 1920 . when the polish army began to retreat during the course of the polish – soviet war , the lithuanians moved to secure what they claimed to be their new borders , set by the soviet – lithuanian peace treaty of july 1920 . the peace treaty granted sejny and surrounding area to lithuania . poland did not recognize this bilateral treaty . ensuing tensions heightened until the outbreak of the polish – lithuanian war . sejny changed hands frequently until it was controlled by polish forces on september 22 , 1920 . the situation was legalized by the suwałki agreement of october 7 , 1920 , which effectively returned the town to the polish side of the border .