The correct answer is Option 2) Conquest by foreigners
Conquest by foreigners an immediate cause for the collapse of the Aztec civilization.
Historians believe that the Aztec Empire was on a steady decline when the Spanish reached South America.
The Aztecs' most powerful days were already behind them and they had sporadically economic and social problems throughout the empire.
For example, many local rebel groups were challenging the central power of the Aztecs while many parts of the large empire were already suffering from food shortages.
However, the arrival of the foreign forces in South America acted as a catalyst and completely destroyed the complex civilization of the Aztecs.