WWII in Colour: Victory in the Pacific Why did Stalin (leader of the Soviet Union) continue to attack after the Japanese surrendered?

Stalin kept attacking because The Soviet invasion came as a fulfilment of Stalin's promise – made to British and American leaders at the Tehran and Yalta conferences – to join the war against Japan following the defeat of Nazi Germany. But it also came in violation of the Soviet-Japanese neutrality pact signed in 1941.

in other words they attacked because Japan technically broke the pact that they had formed between the Soviet union