Final answer:
The United States's first contact with the Islamic World was marked by the Barbary Wars in the early 19th century, not the Louisiana Purchase, War of 1812, or the French Revolution.
Step-by-step explanation:
The marked first contact between the United States and the Islamic World was the Barbary Wars. This series of conflicts occurred in the early 19th century, starting in 1801, and were fought between the United States and several North African states known collectively as the Barbary States. These were the first major conflicts fought by the U.S. overseas and are often considered America's first encounter with the Islamic World. This doesn't count earlier individual contacts by American merchants and explorers, which might not have been official or governmental in nature.
The Louisiana Purchase was significant for other reasons. It doubled the size of the U.S. and raised questions about the expansion of slavery into the new territories. The War of 1812, while significant in its own right, did not represent the first contact with the Islamic World.
As for the French Revolution, in foreign affairs, Americans became deeply divided over it in the 1790s. However, this division was not related to contact with the Islamic world but rather political ideology and international alliances.