Final answer:
The Adams-Onís Treaty of 1819 allowed the United States to acquire Florida from Spain, which had a significant impact on Mexico and much of South America.
Step-by-step explanation:
The Adams-Onís Treaty of 1819 had a significant effect on Mexico and much of South America. Through this treaty, the United States took control of Florida from Spain in exchange for $5 million. This acquisition expanded American territory and allowed for further expansion across the continent.