Known as 'Black Tuesday,' October 29, 1929, saw the catastrophic collapse of the New York Stock Exchange. This event signaled the beginning of the Great Depression, the longest and deepest economic downturn in the history of the industrialized world. Massive unemployment, bank failures, and a total freeze in global trade followed. In the U.S., it led to the 'New Deal' reforms of Franklin D. Roosevelt, while in Europe, the economic misery contributed to the rise of extremist political movements, including the Nazi Party in Germany. The event fundamentally changed the role of government in the economy, establishing the idea that the state must intervene to prevent total financial collapse and provide a social safety net.