The correct answer is a. The Adams-Onís Treaty decided the boundaries between Spanish and U.S. territories. It ceded Florida to the United States and defined the boundary between the United States and Mexico. The treaty also established the western boundary of the Louisiana Purchase.
The treaty was signed on February 22, 1819, by Secretary of State John Quincy Adams and the Spanish Minister to the United States, Don Luis de Onís. It was ratified by the U.S. Senate on February 21, 1821, and by the Spanish Cortes on October 24, 1821. The treaty went into effect on July 25, 1821.
The Adams-Onís Treaty was a major diplomatic victory for the United States. It gave the United States control of Florida, which had been a source of tension between the two countries for years. The treaty also established the western boundary of the Louisiana Purchase, which gave the United States a vast new territory to explore and settle.
The Adams-Onís Treaty was a major step in the expansion of the United States. It helped to secure the country's borders and opened up new opportunities for trade and settlement. The treaty was a major diplomatic achievement for John Quincy Adams, who would later become president of the United States.