Pedro de Alvarado

September 1519 · 5,000 total casualties

The most important reversal of the conquest. Tlaxcala's alliance gave Cortés a secure base, a supply of provisions, and above all an army: Tlaxcalan warriors would outnumber the Spanish by ten or twenty to one in every battle that followed. Tenochtitlan did not fall to 900 Spaniards — it fell to a coalition of the Aztecs' enemies with 900 Spaniards at its head.

November 8, 1519 · 0 total casualties

For months the most powerful state in the Americas was governed by a hostage. Why Moctezuma admitted the Spanish at all remains debated — the old story of a god-king paralysed by prophecy is largely a post-conquest invention, and the likelier explanation is a ruler taking the measure of a small, strange embassy he expected to control.

May 22, 1520 · 1,000 total casualties

Alvarado destroyed in an afternoon what Cortés had spent six months building. Moctezuma, brought out to calm the crowds, was stoned by his own people and died days later; the hostage strategy was finished. From this moment the Spanish were not guests in Tenochtitlan but a trapped garrison in a hostile city.

June 30, 1520 · 6,000 total casualties

The worst defeat any conquistador force ever suffered, and the moment the conquest nearly ended. Cortés lost his artillery, his horses, his plunder, and most of his men. That he survived at all — and returned a year later to take the city — is why the night is remembered by the name the Spanish gave it while weeping under a tree at Tacuba.

July 7, 1520 · 3,000 total casualties

Otumba saved the conquest. A broken force with no firepower left should have been annihilated; instead a single decapitating charge exploited the Aztec practice of directing battle from a visible standard. The road to Tlaxcala stayed open, and Cortés reached his allies alive — with a year to build the army and the fleet that would return.

May 26 – August 13, 1521 · 150,000 total casualties

The end of the Aztec empire and one of the deadliest sieges in human history — perhaps 100,000 or more died of hunger, disease, and fighting. Tenochtitlan, one of the largest cities on earth, was systematically destroyed and Mexico City built on its rubble. The Spanish won the siege at the head of an indigenous army; the war that ended the Aztec empire was fought largely by other Mexicans.