When did the international economy collapse and why- durning the great depression

Many people during the roaring 20s had lots of money and decided to start buying stocks. More and more people bought the stocks until they were valued more than their actual worth. Americans poured their money, sometimes their life savings, into stocks. In October of 1929, the booming American economy came to an abrupt end as the US stock market crashed. Panicky investors tried to sell their stocks. Banks had made loans that people could not repay. Depositors grew nervous about their money and tried to withdraw it all from the banks, leading to bank failures. Businesses went broke, once-busy factories closed, and millions of workers lost their jobs. 

This affected other nations because once America lost it's prosperity and money, they no longer traded. Due to bank failures and factories closures, America did less business overseas, spreading the Great Depression all over.

Hope this helped ^.^ 
ps, this is from my notes. :)