Why can the crisis of 1929, be said the most important in the XXth Century?

       To beginning, if we read newspapers from October 1929, especially the New York Times, we learn that on the 29th of October in 1929, considered as  "the most disastrous in Wall Street's history", people, and above all, the bankers and the brokers could attend a gigantic and virtual collapse of the stock prices, which led to the loss of billons of dollars, in the open market. Indeed, the period which began on the 24th of October, called the Black Thursday, and finished five days later, on the 29th of the same month, the Black Tuesday, was the point of departure of the Great Depression, in other words, the crash in Wall Street which saw the currencies collapsing...became a grant-holder crisis, then an economic one, the most important in the XXth century, paralysing at first the United States of America, then the world. 
      As an extra piece of information, if we study the Farm Prices in the USA between 1928 - the year announcing the crash -, and 1935 - which preceded the Second World War -, ( you could find these figures on the Net : go for examples visiting the very interesting site : http://www.studyworld.com/depression_of_the_1930's.htm ), we can see that all the sectors were hit by it, as the agricultural one ( in seven years, these prices tumbled : in 1930, there were about 24 dollars and about 15 $ in 1934). In fact, the crisis was born in Wall Street, but extended to all the primary sectors industry, like the farming and rural one so - crop prices fell by 60% per cent -, the mining and the forest domains too.  
      Lastly, this mother, brought up in the photo by Dorothea Lange, Migrant Mother, taken in 1936, is a symbol of the Great Depression in the United States of America, which looks like characters in The Grapes of Wrath by John Steinbeck  in 1939 (read Jonh Steinbeck's books ! Are advised : Tortilla Flat, The Grapes of Wrath, East of Eden...), who was inspired by this period : indeed, many wives, mothers had to work with their children in order to feed them: about 69% of women were dependent of their own earnings for their children's survival ( most of the husbands were in war). That's why Florence Owens Thompson, who earned fifty cents a day, embodies all  a category of people, hit by the economic crisis. Moreover, in this photo, we can realize the problem of education : leaving their cities to find work, women brought with them their children who suffered from this situation : most of them couldn't go to school, 20% of them didn't wear clothes, were unkempt and dirty, and between 1930 and 1938, the infant mortality rate increased more than 20 per cent... Look at this photo we've just commented :




We can conclude so, that a day of October in Wall Street threw the United States of America and then the world, into a deep and fatal crisis during many years, paralysing all industry in a long economic slowing down, considerably increasing unemployment rate, and intensifying poverty ; it upset the world ans it is considered nowadays as the most important crisis in the XXth century, that the current one will maybe prolong in the XXIst...We will see...