Shortly after the last post on this topic, U.S. foreign policy has had to do some serious revamping, for on the eve of May 1, 2011, Osama bin Laden, the orchestrator of the largest mass killing of Americans in an act of unprecedented terrorism was found and killed by U.S. Navy Seals.
In my opinion, this seminal achievement by U.S. intelligence and armed forces surpasses even the monumental happenings of "Arab Spring." There are several reasons for this.
First, with bin Laden dead, the U.S. has little logical reason to remain in Afghanistan, and President Obama can begin fulfilling his campaign promise to bring troops home. However, with the government of Afghanistan still not cohesive, and Afghani forces still arguably unready to take over the nation, there are many elements of the transition for foreign policy to contend with.
Secondly, there is the Taliban to consider. In the past, it was unthinkable to consider allowing the Taliban to control any portion of Afghanistan. Now, that thinking is beginning to change. A key Republican address recently conceded that exiting (thus ending the loss of life as well has the millions of dollars being drained from the economy) Afghanistan may mean that the Taliban will re-take some portion of the country.
Thirdly, those politicians who create foreign policy are now having to consider what to do about Pakistan, a country who is supposedly our ally, yet allowed our most wanted fugitive to live within plain sight for many years, making Pakistan, in effect, either "implicit or incompetent."
Then, there is our own willful violation of an allied airspace without notificiation of the ally (Pakistan), which has raised protests from the Pakistani government.
Meanwhile, intelligence and armed forces continue to pursue leads on Al- Qaeda's Number Two Man, Abu Hafs al-Najdi.
I see that your question is tagged with "2011." If you are limiting your question to events that are from this year, the most important events are those that have happened in Egypt, Libya, and the rest of the Middle East.
The movements that have happened and are happening in those countries have had a huge impact on US foreign policy. The US has to deal with, for example, the overthrow of a pro-US autocrat (Hosni Mubarak) in Egypt. The US has to figure out how to act in ways that will A) help Egypt become democratic and B) protect US interests. This is especially difficult because it is hard to know to what extent a more democratic Egypt would be anti-Israel or how "Islamist" it would be.
Nothing else that has happened this year has the same impact on US foreign policy as these uprisings.
I think that you will wind up with a great many responses about this one. In my mind, I would say that the emergence and perceived global threat of terrorism has impacted the foreign policy direction of the United States over the last ten years. With the attacks of September 11, foreign policy took a sharp turn in articulating the elimination of terrorism as one of the fundamental goals in its relationships with external nations. The ability to find organizations that condone terrorism and isolate countries that harbor and support such endeavors became the foundation upon which U.S. foreign policy was constructed. The wars in Iraq and Afghanistan, working in a more closely aligned manner with Pakistan, and even the recent uprisings in the Middle East, specifically concerning Libya, have all featured terrorism as a common link. Its elimination as a direction of the diplomatic and military paths the United States has taken in these instances have helped to define its foreign policy.