Final answer:
The decision to block all American shipping was most influenced by the poor treatment of American seamen, which led to the Embargo Act of 1807.
Step-by-step explanation:
The decision to block all American shipping was most influenced by the poor treatment of American seamen.
During the Napoleonic Wars, both Great Britain and France repeatedly stopped U.S. merchant ships, seizing cargo and sailors. Britain, in particular, would board American ships and impress sailors into their service, regardless of their nationality.
This poor treatment of American seamen led President Jefferson to respond with the Embargo Act of 1807, which prohibited American ships from leaving their ports until Britain and France stopped seizing them on the high seas.