Short answers, pulled from the story.
One study identified 36 Soviet and Russian interventions in foreign elections from 1946 to 2000. Beyond elections, Soviet involvement in regime change included overt military invasions, covert coups, proxy wars across three continents, and the installation of satellite governments across Eastern Europe, as well as operations in Asia, Africa, and Latin America spanning more than seven decades.
Soviet occupation forces prevented non-communist election winners from taking power, took control of interior ministries and police forces, and pressured heads of state to appoint Soviet-approved prime ministers. Hungary, Romania, Bulgaria, Czechoslovakia, and Poland were all converted into Soviet satellite states between 1944 and 1949. In Hungary, the communist party won just 17 percent of the vote in 1945 yet still took power through a Soviet-backed coup.
The Soviet Union invaded Finland on the 30th of November 1939, and the League of Nations judged the attack illegal and expelled the Soviet Union from the organization. Finland repelled Soviet attacks for more than two months at temperatures as low as minus 43 degrees Celsius. The Moscow Peace Treaty of the 13th of March 1940 required Finland to cede 9 percent of its territory, representing 13 percent of its economy, but Finland retained its sovereignty.
Soviet Army tanks entered Budapest in October 1956 under orders from defence minister Georgy Zhukov after protesters demanded free elections, independent courts, and an inquiry into Stalinist abuses. The new government that formed declared its intention to withdraw from the Warsaw Pact, which prompted a full Soviet military re-invasion. Around 200,000 Hungarians fled the country, some 26,000 were put on trial, and Imre Nagy along with Pal Maleter and Miklos Gimes was executed after secret trials in June 1958.
The Brezhnev Doctrine asserted a Soviet right to intervene militarily in any Eastern Bloc state that appeared to move toward capitalism. It was applied when armies from four Warsaw Pact countries invaded Czechoslovakia on the night of the 20th-the 21st of August 1968, after leader Alexander Dubcek launched an Action Program promising press freedom, multiparty government, and limits on secret police power. An estimated 300,000 Czechs ultimately fled the country and Dubcek was replaced in April 1969 by Gustav Husak, who reversed all the reforms.
The Soviet Union backed Vietnam's invasion of Cambodia on the 25th of December 1978 with $1.4 billion in military aid, which peaked at $1.7 billion per year between 1981 and 1985. Moscow also provided Vietnam with $5.4 billion to fund its third five-year economic plan, covered 90 percent of Vietnam's demand for raw materials, and supplied 70 percent of its grain imports. By 1986 the Soviet government began cutting that support, reducing Vietnam's economic aid by 20 percent and its military aid by one-third.