The Second Polish Republic was a country in Eastern Europe. Formed in 1918 after the First World War, the new Poland faced its first challenge against the also newly formed Russian Socialist Republic in the 1920 Polish-Soviet War. After the victory, and a coup, Poland's economy slowly began to grow, and under the leadership of Józef Piłsudski, the military was quickly growing, as he recognized that the USSR, and by 1936, newly formed Nazi Germany, were both a threat to Poland.
On September 1st, 1939, the first shots of the 1939 Polish Defensive War were fired at Westerplatte. Although the Poles were smashed in the initial days of the invasion, Polish forces quickly regrouped, and began battering German forces. Thanks to Piłsudski's foresight, and his buildup of the military, Poland was successfully able to trap several divisions of the Wehrmacht in East Prussia.
Eventually, Poland's cavalry units, now all of which were augmented with the 7TP light tanks, moved into Nazi Germany proper, as other cavalry units from Krakow rushed through Slovakia, and eventually linked up with the units driving from the north, trapping several more divisions of Nazi troops. As bombers continued to pound Berlin, the French and British finally moved in from the west. With Germany now fighting a war on two fronts, they begged the Soviet Union to intervene as per their pact, but Stalin, fearing the collapse of his regime, did not follow through.
By February 4th, 1940, Polish troops linked up with their French and British cohorts at the Elbe. The Defensive War was over. However, the strife in Europe was not over. In 1946, with the majority of Polish troops putting down a pro Nazi uprising in Germany, Stalin attacked from the east, quickly surrounding Warsaw. Declaring an emergency, the Poles drafted all able bodied men ages sixteen through fifty to fight the Soviets while the regular army moved in.
Desperate for more manpower, the Poles even drafted former Nazi soldiers to fight the Soviets. In a deadly seven year war, the Poles were only able to force a peace when units of the 1st Polish Parachute Brigade parachuted into Moscow, and captured nearly three quarters of the Soviet leadership, including Josef Stalin himself. With the war over, Poland began rebuilding itself, and it was only in 1963 that the economy returned to its former state, and the prewar population only was surpassed in 1970.
Eventually, with the collapse of the Soviet Union in 2001, engineered by Poland, the U.S., and various other Western States, the Poles grabbed large swaths of land, liberating Ukraine from the USSR, and taking large amounts of land up to the Urals. Asked by the U.S. to help finish off the Communist threat, Polish troops later aided in bringing down most of the remaining Communist states, including the People's Republic of China, North Korea, and the People's Republic of Kazakhstan.