July 7 in Military History — On This Day

Battle of Otumba

A week after the disaster on the causeways, the battered survivors — wounded, without cannon or crossbows, most of the horses dead — were intercepted on the plain of Otumba by an Aztec army vastly larger. Cortés spotted the enemy commander's standard, charged straight at it with the last of his cavalry, and killed him. The Aztec army, its command signal gone, dissolved.

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.

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Marco Polo Bridge Incident

On the night of July 7, 1937, Japanese troops on maneuvers near the Marco Polo Bridge outside Peking claimed a soldier was missing and demanded entry to the nearby Chinese-held town of Wanping. The Chinese refused. After shots were exchanged in the darkness — their origin still disputed — Japanese forces attacked. The skirmish lasted days, but it was the trigger for an eight-year war that would kill 20 million people.

The Marco Polo Bridge Incident was the spark that ignited the full-scale Second Sino-Japanese War. Although neither government initially wanted full war, the escalation quickly spiraled beyond the control of moderates on both sides. Within weeks, hundreds of thousands of troops were committed and the conflict became irreversible.

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⚔️📍 Lugou Bridge, Beijing, China1937

Marco Polo Bridge Incident — Second Sino-Japanese War Begins

Japanese troops conducting night exercises near the Marco Polo Bridge outside Beijing exchanged fire with Chinese soldiers following a confused incident involving a missing soldier. Japan used the incident as a pretext for a full-scale invasion of China.

The Marco Polo Bridge Incident began the Second Sino-Japanese War, which would kill 20 million Chinese and merge into the broader Pacific War in 1941.

Outcome

Full-scale Japanese invasion of China begins; 20 million killed