On 1 September 1939, Nazi Germany, the Free City of Danzig, the Soviet Union and a small Slovak contingent invaded Poland in a surprise attack, using the devastatingly effective strategy of Blitzkrieg. While bombs fell on Warsaw, invasions were underway from both Prussia in the north (led by von Rundstedt) and Slovakia in the south (led by von Bock). Heavy bombing destroyed railroads, lines of communication and infrastructure, as well as much of the Polish air force on the ground. With such damage and ensuing chaos, a unified Polish response was out of the question. German troops rapidly advanced towards each other from both the north and the south, with infantry behind them, reaching Warsaw in just over a week. Russian troops began invading on 17 September and, by 6 October, Germany and Russia had gained control of Poland.