Having defeated Republican Mitt Romney at home, U.S. President Barack Obama has no shortage of adversaries to grapple with abroad, including the governments of Iran, Syria and possibly China.
The Democratic president's re-election ensures continuity in U.S. foreign policy, but leaves open questions such as whether diplomacy can constrain Iran's nuclear program or whether Israel or the United States might resort to air strikes.
Nor is it obvious whether Obama will be able to sustain his refusal so far to try to tip the scales in Syria's civil war by allowing U.S. arms to flow to the rebels seeking to oust Syrian President Bashar al-Assad.
If events permit, U.S. foreign policy analysts said Obama will continue his "pivot" to Asia, seeking to reorient U.S. policy to take advantage of the projected growth in such nations as China and India and gradually withdraw from the Middle East.
However, both Iran, which the United States and its allies suspect of developing nuclear weapons, and Syria, where a car bomb killed and wounded dozens in the capital, Damascus, on Tuesday, will demand attention.
Martin Indyk, vice president of foreign policy studies at the Brookings Institution think tank, said 2013 could be a decisive year on Iran and suggested Obama's wider commitment to nonproliferation could produce a "focused and assertive" policy.
"It's going to be very high on the agenda," Indyk said. "Preventing Iran from getting nuclear weapons is a critical imperative for bolstering the nonproliferation regime."
Iran denies U.S. accusations that it seeks to develop nuclear weapons under cover of its civilian atomic program, saying its program is for peaceful uses such as generating electricity and producing medical isotopes.
Talks between the major powers and Iran on a diplomatic solution are expected to resume - possibly as early as this month - but it is by no means clear whether one can be fashioned under which Iran might rein in its program.
In an effort to drive Iran to compromise, the United States and the European Union have gone for the jugular - Iran's oil exports - over the last year.
The United States has targeted foreign banks that deal with Iran's central bank, the clearing house for its oil sales, and the European Union has ceased importing Iranian crude entirely.
The United States and Israel, which regards a nuclear-armed Iran as a threat to its existence, have also hinted at the possibility of military strikes against Iran.
In a speech to the United Nations General Assembly in September, Israeli Prime Minister Benjamin Netanyahu suggested that a decision on force could come by next spring.
Tehran's UN mission responded by saying Iran has the means and right to retaliate with full force against any attack.
Israel, presumed to be the region's only nuclear power, has twice destroyed sites it feared could be used to develop atomic weapons - in 1981 in Iraq and in 2007 in Syria.
Obama has said the United States will "do what we must" to Iran from acquiring nuclear weapons and has repeatedly said that all options are on the table - code for the possibility of using force.
James Dobbins, director of the RAND International Security and Defense Policy Center, said he thought Obama might be forced by events to intervene to some degree in Syria, possibly by supplying arms, but was unlikely to strike Iran.
"I don't think it's viable to stand aside if Syria gets worse and unless the Iranians are stupid enough to give us a better rationale for an unprovoked attack, I don't think the administration would do it," Dobbins said.
Analysts said that the overarching challenge for Obama will be to try to shape the international environment to the United States' advantage at a time when the country is deeply in debt, other powers are rising and it faces transnational threats such as terrorism, cyber-attacks and global warming.
"My read of Obama is that he, essentially, wants to turn away from the Middle East and focus on Asia," said Indyk, saying Obama was unlikely to make a fresh run at Israeli-Palestinian peace, nor to make great efforts to shape the outcome in Syria or to deeply engage Islamist governments in Egypt and Tunisia.
"I just don't see those things as high on his agenda versus building a relationship with China, promoting India's rise in Asia and seeking the opportunities that lie in that region of the world," he said.
Despite having referred to China as "both an adversary but also a potential partner," in his final debate with Romney, Obama's prime focus is likely to be to try to find ways to cooperate with, rather than confront, China.
"We will increasingly think of ourselves as a Pacific nation rather than an Atlantic nation," said Jon Alterman, who holds the Zbigniew Brzezinski Chair in Global Security and Geostrategy at the Center for Strategic and International Studies.
World reacts to Obama's re-election
British Prime Minister David Cameron said Wednesday, just after Obama was re-elected, that the United Kingdom and the United States should make finding a way to solve the Syrian crisis a priority.
"Right here in Jordan I'm hearing appalling stories of what is happening inside Syria," Cameron told journalists at a camp for Syrian refugees in Jordan.
"...One of the first things I want to talk to Barack about is how we must do more to try and solve this crisis."
Cameron, who is on a diplomacy and trade visit to the Middle East, said he also looked forward to working with Obama to "kick start the world economy" and push for an EU-U.S. trade deal over the next four years.
Egypt's presidency said on Wednesday it hoped re-elected U.S. President Barack Obama would work for the interests of both the American and Egyptian people.
A few months into first term as president, Obama delivered a speech at Cairo University in June 2009 calling for a "new beginning" between the United States and the world's Muslims.
But many in the region feel let down, saying he did not do enough on issues such Palestinian aspirations for a state.
"We congratulate the American people on their choice and we hope the newly elected U.S. administration will work to achieve the interests of both the American and Egyptian people," presidential spokesman Yasser Ali told Reuters.
He said Mohamed Mursi, an Islamist who is Egypt's first freely elected president, would send a letter to Obama to congratulate him later on Wednesday.
The Arab League on Wednesday called on Obama to use his second term to ensure that peace is reached in the Middle East.
"The U.S. people will be benefit directly if security and peace are fulfilled in the Middle East," Nabil al-Arabi, the head of the 22-member bloc, said in a statement.
"History has proved that in the second term, the [U.S.] president becomes more capable of undertaking major missions and responsibilities at home and abroad."
In a 2009 speech in Cairo, Obama pledged to pursue a two-state solution to the Palestinian-Israeli conflict. However, Arabs say he has done little to keep the pledge.
German Chancellor Angela Merkel on Wednesday led a chorus of European praise for Barack Obama, with the United States' traditional allies looking to yet more openness and better trade ties from the president's second mandate.
"I look forward to continuing this [cooperation], so that both our countries can continue to work side-by-side to master the most important foreign and economic challenges that we face as friends and allies."
Merkel cited the pair's past "close and friendly cooperation" regarding the ongoing financial crisis, peacekeeping in Afghanistan and efforts to control Iran's nuclear program.
Fellow conservative leader David Cameron of Britain stressed cooperation on efforts to revive the world economy and resolve diplomatic conundrums, such as the Syrian conflict, as the key issues facing transatlantic relations over the next four years.
"There are so many things that we need to do: we need to kick start the world economy and I want to see an EU-U.S. trade deal," Cameron said in a statement issued during his current tour of the Middle East.
"Right here in Jordan I am hearing appalling stories about what has happened inside Syria, so one of the first things I want to talk to Barack about is how we must do more to try and solve this crisis," Cameron said.
In Brussels, European Union President Herman Van Rompuy and European Commission President Jose Manuel Barroso said Obama should help them address "global challenges, including in the fields of security and economy." They also highlighted efforts to "unlock the unparalleled potential of the trans-Atlantic market" as a priority.
EU-U.S .relations have been strained by a carbon emissions dispute, while Europe has also come under pressure from Washington to resolve its long-standing debt crisis.
French President Francois Hollande, a socialist, congratulated Obama on his reelection as US president, saying voters had made the choice of "an open America" that believes in solidarity and multilateralism.
"It's an important moment for the United States but also for the world," Hollande said in a message to Obama.
"Your reelection is a clear choice in favor of an open America that shows solidarity and is fully committed to the international stage and aware of our planet's challenges: peace, the economy and the environment," he said.
Swedish Prime Minister Fredrik Reinfeldt praised Obama's "inclusive campaign" but noted that Obama faced major challenges since Congress was politically divided, and it remained to be seen how the president would be able to carry out his economic policy.
Lithuanian Prime Minister Andrius Kubilius said he had "no complaints" about Obama, despite describing himself as a conservative, while Belgian Prime Minister Elio di Rupo, one of Europe's first openly gay leaders, said Americans had opted for "a more just and more tolerant America."
Outside Europe, Chinese leaders hailed the "positive progress" registered in bilateral ties during Obama's previous term, although acommentary by the government's Xinhua news agency said Obama's administration should now "set a more constructive tone in crafting its China policy" over the next four years.
India's leaders said they were looking forward to boosting ties during Obama's second four-year term, while Israel expected the Obama administration to continue its policy of looking after Israel's security and of working to move Israeli-Palestinian peace talks forward.
Obama's victory was also greeted by, among others, predominantly-Muslim Malaysia, Australia, Saudi Arabia and Palestinian leaders.
"We will have Obama and also [Russian President Vladimir]Putin and leaders from China and Japan," he told reporters.
Meanwhile, a Cambodian minister said on Wednesday that Obama would be in the Cambodian capital of Phnom Penh on Nov. 18 for a summit of leaders from Southeast Asian states and partner countries. Information Minister Khieu Kanharith said he did not know how long Obama would be in the country.
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