The Katyn massacre was a mass execution of Polish citizens by the order of Soviet authorities in 1940. About 8,000 of those killed were reserveofficers taken prisoner during the 1939 Soviet invasion of Poland, but the dead also included many civilians who had been arrested for being "intelligence agents and gendarmes, spies and saboteurs, former landowners, factory owners and officials". Since Poland's conscription system required every unexempted university graduate to become a reserve officer, the Soviets were thus able to round up much of the ethnic Polish, Jewish, Ukrainian, Georgian and Belarusianintelligentsia of Polish citizenship. The 1943 discovery of mass graves at Katyn Forest by Nazi German forces precipitated a rupture of diplomatic relations between the Soviet Union and the Polish government-in-exile in London. The Soviet Union continued to deny responsibility for the massacres until 1990. Although the Russian government acknowledged that the NKVD had in fact committed the massacres, it does not consider them a war crime or an act of genocide, as this would have necessitated the prosecution of surviving perpetrators.
Warsaw (Warszawa) is the capital and, with a population of over 1.7 million, the largest city of Poland. Founded in 1300 on the Vistula River, Warsaw became the seat of the dukes of Masovia in 1413. Masovia was annexed by Poland in 1526, and 70 years later, in 1596, King Sigismund III moved his seat from Kraków to Warsaw. The rise in political status was accompanied by strong economic and cultural development. Occupied by Nazi Germany during World War II, Warsaw was the site of the Warsaw Ghetto Uprising in 1943 and the Warsaw Uprising in 1944, followed by a complete destruction of the city. Painstakingly rebuilt in the Communist era, Warsaw is now an increasingly important political and economic hub of Central Europe.