The four classes of political institutions in China are:
1. Imperial China (221 BC - 1912 AD): This period was characterized by the dynastic rule of emperors, who held absolute power over their subjects.
2. Republican China (1912 - 1949): This period saw the end of the imperial system and the establishment of a republican government. However, the country was plagued by political instability, warlordism, and foreign aggression.
3. Communist China (1949 - present): This period began with the establishment of the People's Republic of China under the leadership of the Chinese Communist Party. The country has been ruled by a single party ever since, with a socialist political system and a planned economy.
4. Reform Era (1978 - present): This period saw China's transition from a planned economy to a market-oriented economy, as well as the gradual opening up of the country to the outside world. The political system has also undergone some changes, with a greater emphasis on meritocracy and collective leadership.