Escalation of the conflict appeared imminent, and both sides spent June amassing forces. On July 1 the Japanese force numbered 38,000 troops. The combined Soviet-Mongol force had 12,500 troops. The Japanese crossed the river, but after a three-day battle their opponents threw them back over the river. The Japanese kept probing the Soviet defences throughout July, without success. On August 20 Georgy Zhukov opened a major offensive with heavy air attack and three hours of artillery bombardment, after which three infantry divisions and five armoured brigades, supported by a fighter regiment and masses of artillery (57,000 troops in total), stormed the 75,000 Japanese force deeply entrenched in the area. On August 23 the entire Japanese force found itself encircled, and on August 31 largely destroyed. Artillery and air attacks wiped out those Japanese who refused to surrender. Japan requested a cease-fire, and the conflict concluded with an agreement between the USSR, Mongolia and Japan signed on September 15 in Moscow. In the conflict, the Red Army losses were 9,703 killed in action (KIA) and missing in action (MIA) and 15,952 wounded. The Japanese lost 25,000 KIA; the grand total was 61,000 killed, missing, wounded and taken prisoner. Shortly after the cease-fire, the Japanese negotiated access to the battlefields to collect their dead. Finding thousands upon thousands of dead bodies came as a further shock to the already shaken morale of the Japanese soldiers. The scale of the defeat probably became a major factor in discouraging a Japanese attack on the USSR during World War II, which allowed the Red Army to switch a large number of its Far Eastern troops into the European Theatre in the desperate autumn of 1941. Second World War The Polish Campaign On September 17, 1939, the Red Army marched its troops into the eastern territories of Poland (now part of Belarus and Ukraine), using the official pretext of coming to the aid of the Ukrainians and the Belarusians threatened by Germany, which had attacked Poland on September 1, 1939. The Soviet invasion opened a second front for the Poles and forced them to abandon plans for defence in the Romanian bridgehead area, thus hastening the Polish defeat. The Soviet and German advance halted roughly at the Curzon Line. The Molotov–Ribbentrop Pact, which had included a secret protocol delimiting the "spheres of interest" of each party, set the scene for the remarkably smooth partition of Poland