Most of the early encounters between the European imperialist powers and the local powers were not conventional military confrontations in which two sides fight pitched battles and try to kill a maximum number of other side’s soldiers. The locals in these encounters were psychologically disarmed and were not mentally inclined to launch a full scale war on the Europeans.
The Europeans knew that they had arrived to conquer and plunder, but the locals were clueless about how to deal with the outsiders who had suddenly appeared on their land. In the initial period of the encounters, the locals would be in awe of the strange customs, language, food habits, dresses, weapons, and ways of fighting of the outsiders. Thus, the Europeans had a distinct psychological advantage.
In some contests, 50 to 200 European soldiers, dressed in military costumes and riding horses, could psychologically disarm thousands of locals—in a conventional military battle this sort of feat would be impossible. But in South America, Hernán Cortés and his tiny band of Conquistadors could conquer large territories without any military style opposition from the other side.
Cortés was not a military commander. He never won a pitched military battle in South America. In his lifetime, he never fought or led an army in a pitched military battle against a powerful enemy. He won in South America due to psychological reasons. Cortés would not be effective in any military battle where the other side was not psychologically emasculated and was determined to fight back.
In Europe and the Middle East kind of conflicts, a man like Cortés would be a miserable failure. He would not have survived for an hour against Hannibal, Bohemond, Genghis Khan, or Saladin. Cortés was good at waging a psychological war against primitive and isolated communities. But he was no military commander.