其實簡單的時間點查證很簡單，Google 就有：

1. 經濟大蕭條始於1929 年股市崩盤

2. Smoot–Hawley Tariff Act, was a protectionist trade measure signed into law on June 17, 1930. 其促使大蕭條惡化，而非直接導致大蕭條。

以上。