Before America was a leader politically and economically, it was gold that each country traded the merchandise. The gold was changed to US Dollar because gold is not stable, and many countries did not have much gold. Since then America controls the world economy, and every other countries work hard to manufacture inexpensive items to export to US. And they are paid in US Dollars. It was not so easy for America to take leadership economically because there was different society ideologically, like Soviet Union, East Germany and Main Land China. There were two World Wars, which Involved many countries. America helped other countries no matter how different their societies were. It formed such things as food aid and loans. America always opened its door for other countries to export inexpensive Merchandise to America. America wanted to export US made products to those countries. But many times those undeveloped countries made high duty taxes .
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on the merchandise imported from foreign counties including America. Each country has its own currency but was not stable; therefore they try to obtain US Dollars by exporting cheap merchandise to US. Yes, I think the American economy can save the rest of the world.
The Soviet Union was resolved and the Berlin Wall had fallen down, the World has changed drastically. Europe tried to unit a one large Economic group by making the Euro to be used in associated countries. The Euro seems to play a big role in the world like the US Dollar. In the meantime many undeveloped countries like China became more "Industrialized Countries" who started making sophisticated merchandise like Computers and automobiles. Countries sometimes do not accept Americans ideology religiously, and some religious group like cult groups caused terrorist acts in America like in September 11, 2001, which killed thousand of innocent people who worked in World Trade Center in New York.