The passage primarily discusses the Great Depression and World War II, focusing on the impact of these events on the United States and Canada. Therefore, the correct answer that most closely relates to the passage is:
A. The Great Depression
The passage highlights the financial collapse in 1929, the resulting hardships, Franklin D. Roosevelt's New Deal policies, and the involvement of the United States and Canada in World War II, making it clear that the Great Depression was a significant factor in this history. The other options, the Mexican-American War and the Mexican Cession, are not mentioned in the context of the passage.