The United States and its relations with countries around the world has had a long and varied history. The Oxford Encyclopedia of the Modern World Online has a nice overview of American Foreign Policy with links to major events and issues. There are also articles on the United States Relations with regions, such as Africa, and specific countries.
Paley Reference has a three volume set Global perspectives on the United States : a nation by nation survey at call number E895 .G564 2007
One way to find ideas for political science topics is to see what has already been written.
Political science research is first reported by researchers in academic journals and books. Most research is published and only a few people ever learn about it. Sometimes, the research strikes reporters as having something interesting about it for a more general audience and it will get written about in magazines, newspapers, and blogs. It also helps to have a general grasp of a topic from magazines and newspapers before tackling scholarly research.
For example, Foreign Policy magazine maintains a clear and readable annual Failed States Index that measures the challenges faced by "the worlds most fragile countries." You might look at it for countries to consider as topics, and also look at the methodology they used to compile their report for ideas on where to look for research.
Nonetheless, academic journals, also called scholarly journals and peer-reviewed journals, are the sources of research you should use and refer to in order to support your writing.
But, magazines, newspapers, and blogs are useful for finding topics, reading about them from interesting, engaging writers (academic writers almost never are) and seeing what research is getting attention. Politics and lawmaking are one of the main staples of newspapers and news magazines. Reports and analysis in these differ significantly from the theoretical perspectives of academic journals. But, it is always a good idea to get a good grounding on events before tackling academic research on a topic.
A search on the phrase political science in the database Academic Search Premier gives results for the whole range of types of publication types such academic journals, magazines, and newspapers, each of which you can select to narrow to that format. Again, magazines and newspapers are usually the most readable.
LexisNexis Academic also has major papers from around the world as well as many other sources, such as magazines and transcripts.
Ethnic Newswatch covers ethnic newspapers and scholarly journals devoted to ethnic issues.
CQ Researcher Online is a publication that does excellent balanced reports on all kinds of topics particularly of interest to policymaking-- with lots of help in suggesting other sources. It's both a good source for looking for ideas and looking to see if they have covered a topic you have in mind.
You might also try browsing for references to a topic in magazines and newspapers using a word for the topic and combine it with the phrase "political science." In most cases, this will lead to a reference to a professor of political science that the reporter has contacted to get an expert view. This also gives you the name of a researcher in the area of a topic, which is also a good way to search.