Almost any of the topics here would be good choices for your essay, although some might be stronger choices than others. For each topic, there are some key pros and cons and issues you want to keep in mind:
1) War: This is probably the weakest choice as it is so general. Many different wars have occurred in the past few decades, including several in the Middle East that have affected or been affected by US politics, but there are simply so many different possible wars to cover that it would be hard to write this as a coherent essay.
2) US-China relations: This would be a great topic, because it is clearly focused, with a distinct historical arc from Nixon's initiation of trade with China through various controversies over currency manipulation and intellectual property.
3) Oil markets/OPEC: This would also be a strong and focused choice, as consumer gas prices affect inflation and the popularity of the President.
4) 9/11: This is also a good essay topic as it explains changes in civil liberties and attitudes towards global terrorism.
5) Financial globalization and bond markets: While this is an important area, its effect on politics is subtle and complex, making it somewhat more difficult as an essay topic than some of the other choices.
6) The environment/Pope Francis’ encyclical on climate change: Although Pope Francis' statements have influenced the attitude of some Roman Catholics, they haven't by themselves caused a huge shift in people's attitudes. The environment is a fairly diffuse topic, making this a rather weak subject choice.
7) International organizations: The rise of NGOs has marked a major shift in the structure of aid to developing nations. Another issue is the rise of multi-lateral trade pacts, and various talking shops. You could focus on either of these.
8) International trade: The effect of international trade on US jobs and economy would also be a good topic.
Pick three of the topics. The reason I say three is that you might not find enough data or too much. Take note cards and on each card cite the information to be used, and its focus area (for example, political interest). Keep repeating the process until you have completed your note cards and have enough information to write your paper. I will include a graphic organizer to help you.