Edited sentence: In order to buy goods from abroad developing countries need a hard corrency (dollars or euros or both) which they have to buy by oferring other goods in return, e.The US dollar is only one of the reasons (others being historical, militarilly, political,ect as to why the US is able to have so much debt held by the public, so little foreign reserves when compared with the size of the US economy and the world's biggest trade defict.Unlike other currencies which have to be backed by a handful of other currencies or gold lest inflation kicks in, the north american dollar is backed by the sheer size of the US economy so that the Federal Reserve which is a private bank is able to print money at will at levels that the world markets tolerate indeed is depended on.petroleum is bought and sold with dollar everywhere in the world