After the early successes of Operation Barbarossa (the Nazi invasion of the Soviet Union), the Germans were surrounded and defeated at Stalingrad. The Soviet army pushed westward, forming the Kursk 'bulge' or salient. Operation Citadel was the 1943 Nazi offensive to pinch off the Kursk bulge. In response to the German buildup, the Soviets prepared defenses in depth. What resulted was a decisive strategic defeat for the Nazis, and they were never able to recover. The Russians continued to press toward the west and eventually captured Berlin.