What religion did the Mayan or Azteca believe in? What made them believe in a God?

Hundred of years before the Spanish Exploration discover Mexico and Central America, there were Mayan who believe in a God, but what God? According to Historian, they made sacrifice by killing and taking the heart of a young lad and a young baby. Who were their God? To whom were they worshipping to? What Church or religion did they go to or believe? The same with Azteca. Who did they worshipping to? How about the Native Indian, did they believe in a divine spiritual God? Also in China back thousand of years ago, What God or religion did they believe in? What made them believe what they believe? What's your opinion?