Why did his defeat at Waterloo spell the end of Napoleon's rule? He lost the support of the army, and without that he could not rule.
The leaders of Napoleon’s army were fearful of yet another defeat, so they did not fight as fiercely.
Napoleon was seen by his troops as an unfit military leader after the loss at Russia.
Several of Napoleon’s enemies combined their forces at Leipzig to defeat him.

He lost the support of the army, and without that he could not rule.

Explanation:

Because "Reportedly fatigued and in poor health during the Belgian campaign, Napoleon committed tactical errors and acted indecisively. He also was blamed for appointing inadequate commanders." and "He reportedly rode away from the battle in tears." (History.com, 2018)

A:  He lost the support of the army, and without that he could not rule.

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