Based on the information in the excerpt, the most supported inference is: The attacks on American shipping vessels led to a build-up of an American naval force.
The excerpt describes how American shipping was almost defenseless against French privateers due to the tensions between France and the United States. However, it also notes that by 1800, armed merchantmen and U.S. warships were actively working to clear the sea-lanes, indicating a response to the need for protection and an increase in naval capabilities as a result of the conflict at sea. This aligns with the inference about the build-up of the American naval force.