摘要
The development of the United States of America in its history over the past more than 200 years demonstrates that, the strategic line of thought of this nation is rather clear. In other words, America is a "nation that is never content. " This can be seen from its development from thirteen colonies to a big power stretching cross two oceans, then the only superpower in today’s world. The words and deeds of U. S. important political figures and public opinions as well reveal that at pre-
