Final answer:
Between 1850 and 1950, the U.S. national debt was significantly influenced by wartime spending, with major contributions from the Civil War, World War I, and World War II, as well as borrowing during the Great Depression for relief and public works.
Step-by-step explanation:
The changes in national debt between 1850 and 1900 were largely influenced by wartime expenditures. Significant events that increased the debt included the Civil War, Spanish-American War, and other smaller conflicts. Between 1900 and 1950, the U.S. government continued the trend of increasing its debt during the World Wars, notably World War I and World War II. These wars necessitated extensive borrowing to fund the military efforts, which substantially raised the national debt. However, during the Great Depression, the federal government also borrowed heavily to finance public employment projects and relief efforts. It's worth noting that while the federal spending during the Depression was higher than in any other peacetime period, it was still less than the expenditure during the World Wars.