Question: Where did the leader, who claimed that the republic that was coming to an end had become an imperialist power, declare that he would intervene in the Korean conflict?

Knowledge 1: Dissolution of the Soviet Union
On December 8, the leaders of Russia, Ukraine, and Belarus secretly met in Belavezhskaya Pushcha, in western Belarus, and signed the Belavezha Accords, which proclaimed the Soviet Union had ceased to exist and announced formation of the Commonwealth of Independent States (CIS) as a looser association to take its place. They also invited other republics to join the CIS. Gorbachev called it an unconstitutional coup. However, by this time there was no longer any reasonable doubt that, as the preamble of the Accords put it, "the USSR, as a subject of international law and a geopolitical reality, is ceasing its existence." [SEP] Knowledge 2: Korean War
In April 1950, Stalin gave Kim permission to invade the South under the condition that Mao would agree to send reinforcements if they became needed. Stalin made it clear that Soviet forces would not openly engage in combat, to avoid a direct war with the Americans. Kim met with Mao in May 1950. Mao was concerned that the Americans would intervene but agreed to support the North Korean invasion. China desperately needed the economic and military aid promised by the Soviets. At that time, the Chinese were in the process of demobilizing half of the PLA's 5.6 million soldiers. However, Mao sent more ethnic Korean PLA veterans to Korea and promised to move an army closer to the Korean border. Once Mao's commitment was secured, preparations for war accelerated. [SEP] Knowledge 3: History of Russia
Peter the Great died in 1725, leaving an unsettled succession, but Russia had become a great power by the end of his reign.
Knowledge 1: Dissolution of the Soviet Union
On December 8, the leaders of Russia, Ukraine, and Belarus secretly met in Belavezhskaya Pushcha, in western Belarus, and signed the Belavezha Accords, which proclaimed the Soviet Union had ceased to exist and announced formation of the Commonwealth of Independent States (CIS) as a looser association to take its place. They also invited other republics to join the CIS. Gorbachev called it an unconstitutional coup. However, by this time there was no longer any reasonable doubt that, as the preamble of the Accords put it, "the USSR, as a subject of international law and a geopolitical reality, is ceasing its existence." [SEP] Knowledge 2: Korean War
In April 1950, Stalin gave Kim permission to invade the South under the condition that Mao would agree to send reinforcements if they became needed. Stalin made it clear that Soviet forces would not openly engage in combat, to avoid a direct war with the Americans. Kim met with Mao in May 1950. Mao was concerned that the Americans would intervene but agreed to support the North Korean invasion. China desperately needed the economic and military aid promised by the Soviets. At that time, the Chinese were in the process of demobilizing half of the PLA's 5.6 million soldiers. However, Mao sent more ethnic Korean PLA veterans to Korea and promised to move an army closer to the Korean border. Once Mao's commitment was secured, preparations for war accelerated. [SEP] Knowledge 3: Imperialism
Trotsky, and others, believed that the revolution could only succeed in Russia as part of a world revolution. Lenin wrote extensively on the matter and famously declared that Imperialism was the highest stage of capitalism. However, after Lenin's death, Joseph Stalin established 'socialism in one country' for the Soviet Union, creating the model for subsequent inward looking Stalinist states and purging the early Internationalist elements. The internationalist tendencies of the early revolution would be abandoned until they returned in the framework of a client state in competition with the Americans during the Cold War. With the beginning of the new era, the after Stalin period called the "thaw", in the late 1950s, the new political leader Nikita Khrushchev put even more pressure on the Soviet-American relations starting a new wave of anti-imperialist propaganda. In his speech on the UN conference in 1960, he announced the continuation of the war on imperialism, stating that soon the people of different countries will come together and overthrow their imperialist leaders. Although the Soviet Union declared itself anti-imperialist, critics argue that it exhibited tendencies common to historic empires. Some scholars hold that the Soviet Union was a hybrid entity containing elements common to both multinational empires and nation states. It has also been argued that the USSR practiced colonialism as did other imperial powers and was carrying on the old Russian tradition of expansion and control. Mao Zedong once argued that the Soviet Union had itself become an imperialist power while maintaining a socialist façade. Moreover, the ideas of imperialism were widely spread in action on the higher levels of government. Non Russian Marxists within the Russian Federation and later the USSR, like Sultan Galiev and Vasyl Shakhrai, considered the Soviet Regime a renewed version of the Russian imperialism and colonialism.
Knowledge 1: Dissolution of the Soviet Union
On December 8, the leaders of Russia, Ukraine, and Belarus secretly met in Belavezhskaya Pushcha, in western Belarus, and signed the Belavezha Accords, which proclaimed the Soviet Union had ceased to exist and announced formation of the Commonwealth of Independent States (CIS) as a looser association to take its place. They also invited other republics to join the CIS. Gorbachev called it an unconstitutional coup. However, by this time there was no longer any reasonable doubt that, as the preamble of the Accords put it, "the USSR, as a subject of international law and a geopolitical reality, is ceasing its existence." [SEP] Knowledge 2: Korean War
On 27 June 1950, two days after the KPA invaded and three months before the Chinese entered the war, President Truman dispatched the United States Seventh Fleet to the Taiwan Strait, to prevent hostilities between the Nationalist Republic of China (Taiwan) and the People's Republic of China (PRC). On 4 August 1950, with the PRC invasion of Taiwan aborted, Mao Zedong reported to the Politburo that he would intervene in Korea when the People's Liberation Army's (PLA) Taiwan invasion force was reorganized into the PLA North East Frontier Force. China justified its entry into the war as a response to "American aggression in the guise of the UN". [SEP] Knowledge 3: History of Russia
Peter the Great died in 1725, leaving an unsettled succession, but Russia had become a great power by the end of his reign.

Answer: the Politburo