Short answers, pulled from the story.
Marxism-Leninism was created by Joseph Stalin in the Soviet Union during the 1920s, based on his synthesis of classical Marxism and Leninism. His 1926 text Concerning Questions of Leninism formally presented it as a distinct ideology, and the 1938 textbook History of the Communist Party of the Soviet Union (Bolsheviks) popularised it widely.
China, Cuba, Laos, and Vietnam currently hold Marxism-Leninism as the official ideology of their ruling parties, though each gives it different interpretations in practice. North Korea's state ideology, Juche, derives from Marxism-Leninism but constitutional references to it were removed in 1992 and 2009.
The Sino-Soviet split of 1956-1966 severed diplomatic, political, cultural, and economic relations between the Soviet Union and China, arising from ideological and nationalist tensions after Khrushchev's de-Stalinisation. It produced competing claims to leadership of world communism, contributed to Maoism developing as a distinct tradition, and later caused the Sino-Albanian split in the 1970s when Albania's Enver Hoxha rejected Mao's 1972 meeting with President Nixon.
On the 25th of February 1956, at the 20th Congress of the Communist Party of the Soviet Union, Khrushchev delivered On the Cult of Personality and Its Consequences, condemning Stalin's dictatorial excesses including the Great Purge of 1936-1938. Khrushchev presented de-Stalinisation as a restoration of Leninism and dismantled the Gulag system of forced-labour camps as part of this process.
Historians split between traditionalists, who stressed the totalitarian nature of communist states and Stalin's near-absolute power, and revisionists, who emerged from the 1960s and argued that the Soviet leadership had to adjust to real social forces and that the totalitarian model was oversimplified. Scholars have also debated whether the Stalin-era Soviet Union (1924-1953) represented state capitalism, bureaucratic collectivism, state socialism, or a unique mode of production.
Marxist-Leninist movements shaped major Cold War conflicts across both regions. In Asia, the Viet Minh defeated French colonial forces and North Vietnam launched the Tet Offensive on the 30th of January 1968, eventually leading to the fall of Saigon on the 30th of April 1975. In Latin America, the Cuban Revolution of 1953-1959 established a Soviet-allied state, and Nicaragua saw the Sandinista National Liberation Front win power in 1979 before facing a Reagan-sponsored Contra War that concluded with the Tela Accord in 1989.