The Great Depression (1929-mid 1930s) stemmed from several interconnected causes:

1. Agricultural Overproduction: Post-WWI recovery and global overproduction created a grain glut, plummeting prices and ruining farmers.
2. Stock Market Crash: A 1920s speculative boom, often with borrowed money, climaxed in the October 1929 crash. This decimated fortunes and consumer confidence, halting investment.
3. Fragile Banking System: US banks, deeply involved in speculative and international loans, collapsed. Panic-driven savings withdrawals triggered widespread bank failures and a severe credit crunch.
4. US Protectionism & Loan Withdrawal: High US import tariffs crippled world trade. Critically, US lenders withdrew vital loans from Europe, precipitating European bank failures and currency collapses, spreading the crisis globally.