Approved for public release, distribution is unlimited / The end of the Cold War and the September 11th 2001 attacks changed the strategic environment of the world. New socio-political realities increased the use of armed forces. The War on Terror brought the necessity of expeditionary warfare even to countries whose security doctrine had been so far exclusively focused on territorial defense. Poland is one such country. Throughout Polish history, there have been no expeditionary operations. New requirements after 1999 generated the necessity for reforms in Armed Forces of Poland. Since expeditionary warfare has never been practiced by Polish Army before, the reform process needs to be strongly coordinated with such military forerunners as the US Army. The thesis presents a study of contemporary war and its effects on force structure. It also shows how the US Army has reacted to the changing character of warfare. Such reforms as the Stryker Brigades, Army XXI and "Army After Next" program are analyzed in order to assess which of these solutions can be used in Polish Army reforms. The current capabilities of the Polish Army are also assessed in order to judge the background for military reforms in Poland. Finally a recommendation for reforms in Polish Army is made. / Captain, Polish Army