Fear and confidence.  These two very human factors make up the stability of the global market.  Whenever people begin to lose faith in the market, the market suffers.  People stop spending money and horde it all away.  This of course causes businesses to lose revenue.  When they lose enough revenue, businesses are forced to lay off workers.  Of course unemployed workers have less money to spend so the entire vicious cycle continues.

Now, due to globalization, the market of almost every country affects another.  When countries are beginning to lose revenue in their market it seems to make sense to them to pass measures to ensure that domestic products are being purchased over foreign products.  However, it has been proven that the Great Depression was made even worse when legislation like that was passed.

This is why protectionism is so dangerous and frowned upon by the global community.  The European Union has steadily insisted the United States open up its gambling market to online casinos.  The European Commission has threatened to bring its complaints before the World Trade Organization if the United States does not quickly pass some sort of legislation that regulates online casinos.

The legislation that ended up deepening the Great Depression was the Smoot-Hawley Tariff Act of 1930.  In a blind dash to stimulate domestic product, the tariff introduced higher taxes on many major imports.  This of course was to discourage the purchase of imported goods and encourage the purchase of products made in the United States.