Final answer:
The statement that Jefferson's measures of economic pressure were successful is false. The Embargo Act of 1807 led to U.S. economic hardship and did not change British or French policies, leading to its repeal in 1809.
Step-by-step explanation:
The assertion that Jefferson's efforts to use economic pressure to resolve the conflicts with Britain and France were successful is false. President Thomas Jefferson's administration enacted the Embargo Act of 1807, which aimed to exert economic pressure by prohibiting American ships from trading in all foreign ports. The idea was to force Britain and France, who were at war with each other and impeding American trade, to respect U.S. neutrality and rights. However, the plan backfired, causing significant economic hardship in the U.S. and was particularly damaging to American merchants. It did not succeed in changing British or French policies and instead led to increased tensions. The embargo was so unpopular and ineffective that it was repealed in 1809 during the last days of Jefferson's presidency. The failure of the Embargo Act highlighted the limitations of economic coercion as a diplomatic tool during this period.