▁War . ▁Se j ny ▁changed ▁hands ▁frequently ▁until ▁the ▁Su w ał ki ▁Ag re ement ▁of ▁October ▁ 1 9 2 0 , ▁which ▁left ▁Se j ny ▁on ▁the ▁Polish ▁side . ▁The ▁u pr ising ▁und erm ined ▁the ▁plans ▁of ▁Polish ▁leader ▁Jó zef ▁Pi ł s ud ski ▁who ▁was ▁planning ▁a ▁coup ▁d ' état ▁in ▁Lith u ania ▁to ▁replace ▁the ▁Lith uan ian ▁government ▁with ▁a ▁pro - Pol ish ▁cabinet ▁which ▁would ▁agree ▁to ▁a ▁union ▁with ▁Poland ▁( the ▁proposed ▁Mi ędz ym or ze ▁feder ation ). ▁Because ▁the ▁Se j ny ▁U pr ising ▁had ▁prompt ed ▁the ▁Lith uan ian ▁intelligence ▁to ▁intens ify ▁its ▁investig ations ▁of ▁Polish ▁activities ▁in ▁Lith u ania , ▁they ▁discovered ▁plans ▁for ▁the ▁coup ▁and ▁prevent ed ▁it , ▁arrest ing ▁Polish ▁sympath izers . ▁These ▁host ilities ▁in ▁Se j ny ▁further ▁stra ined ▁the ▁Polish – L ith uan ian ▁relations . ▁ ▁Event ually , ▁Poland ▁and ▁Lith u ania ▁reached ▁an ▁agreement ▁on ▁a ▁new ▁border ▁that ▁left ▁Se j ny ▁on ▁the ▁Polish ▁side ▁of ▁the ▁border . ▁The ▁Polish – L ith uan ian ▁border ▁in ▁the ▁Su w ał ki ▁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 ▁Su w ał ki ▁had ▁been ▁various ly ▁part ▁of ▁Lith uan ian , ▁Polish