Final answer:
The strong opposition from European powers and the invasion of France by foreign armies were the main causes of Napoleon's defeat in Europe in 1814.
Step-by-step explanation:
Napoleon's defeat in Europe in 1814 was primarily caused by a combination of strong opposition from European powers and the invasion of France by foreign armies.
After a series of failed military campaigns, including a disastrous invasion of Russia, Napoleon was forced to abdicate his throne in 1814. European powers formed a coalition against him and invaded France, leading to his defeat.
Internal conflicts within France and a lack of military strategy may have also contributed to Napoleon's defeat, but they were not the primary causes.