Final answer:
The British refusal to allow American ships to enter European waters was a key cause of the War of 1812.
Explanation:
The British refusal to allow American ships to enter European waters best completes the graphic organizer showing the causes of the War of 1812. This restriction, combined with the impressment of American sailors by the British navy and the British refusal to acknowledge American neutrality, significantly contributed to the tensions that led to the War of 1812.
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