China became a communist country because of the war and fighting the people faced. As a result of the war the people were Vulnerable which gave the communist party a chance to rule.
Chairman Mao Zedong of the communist party seized the opportunity and took power from the Kuomintang party when they had become weak and trying to recover from the World War II.
At the time of his ruling the economic in China was slow. Chairman Mao Zedong created a new party which was the Republic of China in 1 October 1949.