Why did the U.S. Army expand during the XYZ Affair and the Quasi-War with France?

The U.S. Army expanded during the XYZ Affair and the subsequent Quasi-War with France primarily as a defensive response to the threat of open conflict with the French government.12

In 1797, the United States dispatched ministers to France to negotiate a commercial agreement to protect American shipping, but they were met with demands for bribes and loans, an incident that became public in 1798. This revelation caused a significant public outcry in the United States, leading to widespread preparations for war.1

In response to these heightened tensions, the U.S. government took steps to bolster its military capabilities. The regular army, which had fluctuated in size depending on immediate threats, was expanded to nine regiments in 1798 to address the crisis. This period of undeclared naval warfare saw the Federalist Party, which held power at the time, sponsor strong defense and internal-security legislation to protect the nation's interests against French aggression. Although formal war was ultimately avoided and the situation was settled by the Convention of 1800, these defensive measures were a direct reaction to the diplomatic breakdown and the perceived necessity of securing the young nation.231