To be honest, at the moment, I know more about the importance of being a member of the World Trade Organization (WTO) for China, than I do for the United States. That's curious, isn't it? However, during my time in China, there was great enthusiasm about China's entry in WTO. It has very broad implications as a part of China's "opening up" policy, especially in terms of the economy.
While I am a very strong internationalist, I never thought a great deal about the US involvement in WTO before coming to China. As a major superpower, I assume that WTO membership is important for the US economy, but I am not very sure about that or why. The 2002 decision by the Bush administration in the US to place a tariff up to 30% on steel imports for a three year period is clearly an economic protectionist measure, and seems to me to violate the WTO regulations. I am aware that the European Union, Japan, and China have all protested this tariff, and that it is possible that the WTO might be called upon to decide on this matter. So, this is obviously a problem for the US and other countries who export steel, which hopefully can be solved through negotiations, or by WTO decisions.
It would seem that the WTO might in fact be more likely to lead to a semi-world government structure in economics than the US is in political areas, since decisions by the WTO are binding on participating countries.