Final answer:
John Adams' greatest accomplishment as president was avoiding war with France through the XYZ Affair.
Step-by-step explanation:
John Adams' greatest accomplishment as president was avoiding war with France. This achievement is commonly known as the XYZ Affair. In the late 1790s, France began seizing American ships, escalating tensions between the two nations. Rather than going to war, Adams pursued diplomacy and successfully negotiated a peaceful resolution to the conflict. His ability to prevent a military confrontation with France is regarded as a significant accomplishment during his presidency.
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