Final answer:
The large, highly populated country that became Communist is the People's Republic of China, influenced by the ideology of Marx and Engels and becoming a key player in the global divide during the Cold War.
Step-by-step explanation:
The large, highly populated country that turned Communist is the People's Republic of China. After significant revolutionary movements, China officially embraced communism in 1949 under the leadership of Mao Zedong. However, the concept of communism originally stems from the works of Karl Marx and Friedrich Engels, who advocated for a complete societal restructure to allow the working class, the proletariat, to control the means of production. Barriers erected by ideological differences between capitalist and communist countries fueled the Cold War, with the Soviet Union and the People's Republic of China on one side, pitted against the United States and other western democracies.
Throughout the 20th century, communism expanded beyond the Soviet Union, influencing countries such as Vietnam, North Korea, and Cuba. Contrastingly, in the post-Cold War era, many countries of Eastern Europe have shifted from communist dictatorships to integrated market economies, with Romania being one example. The legacy of communism in these nations and their transitions highlight the complex political and economic dynamics of the 20th century.