Which event had the greatest impact on the size of the United States?

• A. The Louisiana Purchase
• B. The Civil War
• C. The Annexation of Hawaii
• D. The Lewis and Clark Expedition

Answer: (A)

Expanding the country’s land area changes its size more than anything else. The Louisiana Purchase in 1803 added about 828,000 square miles of territory from France, nearly doubling the United States’ size at the time and opening vast lands for future settlement and statehood. The Civil War reshaped governance, society, and economics but didn’t change land area. The annexation of Hawaii added only a small portion of land, and the Lewis and Clark Expedition was an exploration voyage that mapped the land rather than enlarging it. So, the Louisiana Purchase had the greatest impact on how large the United States became.