EN
A state border is most often defined as a line perpendicular to the surface of the earth, separating the territory of one state from other states or from areas not belonging to any state. The legal regulations of state borders are a result of wars, geographical factors, defense strategy, economic and communication development as well as of tradition. Pol-and is an example of a state which often changes its boundries, moving its territory to the east or to the west, making wars and concluding bor-der agreements with other countries. After World War One, Polish bor-ders were based on the Treaty of Versailles Conference of 1919 and the treaty signed with Russia in 1921. The borders created after World War Two were based on the resolutions of the Potsdam Conference of 1945. Polish delegations have taken an active part in both conferences. Joining the European Union in 2004 and the Schengen area resulted in certain changes in the role of state borders. The eastern border became the EU border and the western and southern borders became internal borders. Around the world we can observe aspirations towards creating new states. Ethnic, economic and military issues influence changes in nation-al borders. National borders are a very important factor in the existence, functioning and the role of individual states.