The people of this city planned to kill Cortes in his sleep when he found out Cortes killed 3000 people and burned a large portion of the city

The city you are referring to is likely Tenochtitlán, the capital of the Aztec Empire. Hernán Cortés, the Spanish conquistador, led an expedition that resulted in the fall of the Aztec Empire in the early 16th century.

Following a series of conflicts and betrayals, including the killing of Moctezuma II and the subsequent attack on the Aztec capital, Cortés and his forces engaged in brutal warfare against the city's inhabitants. The siege of Tenochtitlán culminated in the Noche Triste (the "Night of Sorrows") in June 1520, when Cortés and his men attempted to flee the city after suffering heavy losses, leading to significant bloodshed.

The people of Tenochtitlán indeed plotted against Cortés and his men due to these atrocities, including the massacre of thousands of Aztec warriors and civilians. The Spanish conquest was marked by significant violence and destruction, resulting in the eventual fall of Tenochtitlán in August 1521.