There is a subject-verb agreement problem in the first sentence.
The United States must increase its role in the global community by getting more involved with its efforts to ensure global peace and security through global communication such as with the United Nations, Global Summits and Conferences, through which negotiations and agreements can be reached and implemented that, would meet each nations interest who are involved. This sentence is WAY TOO LONG; you need to break it up into at least three sentences if you expect anyone to follow your thoughts successfully.
Immigration to the United States has brought cultural, economic, and religious diversity that must be addressed in order for the United States to maintain a position as a world leader. "must be addressed" how? You need specifics here.
The United States role in the global community was shaken with the current administrations unilateral approach to its foreign policies. There are two possession problems in this sentence; also you need to be specific -- what do you mean (in detail) by "unilateral approach"?
Go through the rest of your paper and look for additional places where there are general statements made without follow-up detail.
Also use this page for any further mechanical help you many need (such as with possessive nouns):
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us history - explain the role of the U.S. in the emerging global community.
us history - explain the role of the U.S. in the emerging global community?
history - explain the role of the U.S. in the emerging global community.
history - Explain the role of the U.S. in the emerging global community
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