Who sent troops to north korea apex?

China

Explanation:

The Korean War was a  conflict between the Democratic People’s Republic of Korea, known as North Korea, and the Republic of Korea, known as South Korea. By June 1950, North Korea, with support from the Soviet Union, invaded the South.

That´s when the war reached international dimensions, as the United Nations and the United States joined the South Koreans side in war, while the People’s Republic of China came to North Korea’s aid.

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social contract theory, nearly as old as philosophy itself, is the view that persons' moral and/or political obligations are dependent upon a contract or agreement among them to form the society in which they liv