China has an abundance of natural resources such as coal, iron, lead and gold. It was has good soil and a warm climate for growing foods. All of these materials are in high demand from other countries.
Other countries may be landlocked and this is makes them more diffucult to trade with therefore they're less liekly to make as much money.
The United States is one of the richest countries in the world which geologically in a good location as it has many shipping points. It also has good relationships with most other countries.