President-elect Donald Trump declared during his presidential campaign that he would pursue an “America First” foreign policy approach in the White House, but the reality is that few of the problems he’ll inherit lend themselves to simple solutions.

The terror threat is among them -- over the course of a single day last week, there were attacks in Ankara, Berlin and Zurich, with the Islamic State in Iraq and Syria (ISIS) claiming responsibility for the truck rampage in Germany.

Mr. Trump has already waded into foreign policy debates during his transition and while he has hinted at his foreign policy approach for certain regions, experts say he hasn’t shown a clear-cut strategy for others. Here are some of the top foreign policy challenges he’ll face next year:

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Syria

Mr. Trump will enter the White House next month nearly six years after the Syrian civil war erupted and while he has criticized the Obama administration’s somewhat hands-off posture there, one expert says it will likely be adopted by the new administration.

“I think that the risk aversion on militarizing the U.S. role on Syria that the Obama administration displayed will continue under the Trump administration,” said Aaron David Miller, vice president for new initiatives at the Woodrow Wilson International Center for Scholars, who has helped advise Democratic and Republican secretaries of state on Middle East policy. “I suspect, based on everything he said on ‘America First,’ he’s going to be very reluctant to get involved in the weeds in reconstructing Syria.”

In November, Mr. Trump indicated that he would likely cut off U.S. support for moderate Syrian rebel groups once he takes office and focus instead on targeting ISIS. He’ll also have to decide what posture to adopt toward President Bashar al-Assad’s regime and Russia, which has helped fight opposition forces, and he’ll have to decide how to deal with Raqqa once it’s liberated from ISIS control.

Syria’s humanitarian crisis is part of the conundrum. More than 13 million people are in need of humanitarian assistance and more than 6 million are internally displaced by violence, the United Nations says, and thousands of civilians have been evacuated from Aleppo in recent weeks. Earlier this month, Mr. Trump said his administration is going to help build “safe zones” in Syria.

Despite the announcement, he made clear on the campaign trail that his administration would block people from entering the U.S. from places with a history of terror ties. He has also blasted the Obama administration for admitting more than 10,000 Syrian refugees into the U.S. over the last year.

Russia

The president-elect will have to deal with Russian President Vladimir Putin, whose relations with the West have deteriorated since his government’s illegal seizure of Crimea in 2014 and its support of armed separatists in eastern Ukraine.

Mr. Trump has signaled he’d like to follow through on his promise to improve relations with Russia by nominating ExxonMobil CEO Rex Tillerson, who has close ties with Russia, as his secretary of state.

He also recently called the the U.S. intelligence community’s assessment that Russia tried to help his candidacy “ridiculous.”

While he’s demonstrating he wants to achieve a better relationship with Russia, Vice President-elect Mike Pence and Defense Secretary nominee Gen. James Mattis (ret.), as well as congressional mainstream Republicans could mitigate any action taken in that direction.

“I worry, if he goes with his instincts. I will be more comfortable if he heeds the advice that he’s likely to get from the vice president-elect and the secretary of defense and maybe the secretary of state,” said Steven Pifer, senior fellow the Brookings Institution’s Center on the United States and Europe.

Mr. Trump and his advisers, however, have raised the possibility of removing sanctions the U.S. has imposed on Russia for two years, and he’ll have to decide whether to renew them in March.

“If President Trump comes in and lifts the American sanctions that are on Russia, my guess is it’s going to be very hard for [German] Chancellor [Angela] Merkel and others in the European Union to hold the line in Europe,” Pifer said. “The West would have given up a huge piece of leverage it has over Russia to try to persuade Russia to try to change its policy toward eastern Ukraine in particular, but also toward Crimea.”

The Trump administration also might not see eye-to-eye with Russia on issues like undoing the Iranian nuclear deal, as Mr. Trump has proposed. Russia helped negotiate the agreement and wouldn’t be likely to support pulling out.

China

Mr. Trump will face a number of challenges with China: friction over trade and economic issues, the cybersecurity threat, its militarization of the South China sea, its pressure on Taiwan and its unwillingness to put pressure on North Korea to give up its nuclear weapons.

He raised eyebrows when he took a congratulatory call from the president of Taiwan after the election and he later said that the U.S. is not bound by the One-China policy -- a diplomatic understanding that has defined the relationship between Washington and Beijing for more than 40 years.

“I don’t know why we have to be bound by a One-China policy unless we make a deal with China having to do with other things, including trade,” Mr. Trump said on “Fox News Sunday.” “I mean, look, we’re being hurt very badly by China with devaluation, with taxing us heavy at the borders when we don’t tax them, with building a massive fortress in the middle of the South China Sea, which they shouldn’t be doing, and frankly with not helping us at all with North Korea.”

The president-elect has also vowed he’d declare China a currency manipulator as soon as he takes office, a promise that is on his campaign website.

Bonnie Glaser, senior adviser for Asia at the Center for Strategic & International Studies, said the Trump team doesn’t seem to have a full strategy yet on China.

“It looks to me like Trump is trying to keep China off balance, to try and signal that he’s not necessarily going to conduct business as usual in the same way that it has been conducted over the last eight years under Obama and that he thinks it can appears that he can gain some leverage by signaling a willingness to confront China,” she said.

North Korea

For the last several months, North Korea has been firing off multiple ballistic missiles and analysts believe that President Obama warned Mr. Trump about the serious threat posed by North Korea during their private 90-minute meeting at the White House following the election.

Glaser said the president-elect, however, seems to lack a plan on North Korea since it’s “not an issue that Trump knows a lot about.” The concern for the U.S., she said, is that the North Koreans could pose an existential threat to the homeland if they can make a nuclear warhead that can potentially reach U.S. territory.

“Do we have a strategy that focuses on defense? Do we take a much more aggressive posture against North Korea?” Glaser wondered about Trump’s plan. “Some people are raising the possibility of a preemptive strike on a missile, if it’s on a launchpad, because we don’t know what’s atop that missile, whether it’s a satellite or a nuclear warhead. There may be some discussions about whether we really need to try to cut off trade and harm North Korea’s economy, go beyond sanctions that are really focused on depriving North Korea of weapons of mass destruction.”

Europe

Mr. Trump faces an evolving Europe whose postwar framework could be threatened by Russia and a wave of far-right leaders. This comes as the United Kingdom deals with the process of withdrawing from the European Union after the Brexit vote this year.

“Europeans will be looking for American leadership and engagement,” said James Cunningham, a former U.S. ambassador who has worked for NATO and the U.S. embassy in Rome.

The president-elect’s approach toward Europe, Pifer added, will be shaped by his approach toward Russia. Mr. Trump will have to decide, for example, whether NATO should beef up its presence in the Baltic states and Poland to defend them against Russia. But if Trump shifts current U.S. policy on Russia to improve relations, it could create rifts within the European Union, which Pifer predicts would create problems.

“I’m worried. I can see an outcome that if he listens to the Republican mainstream foreign policy, you’ll see some changes but it won’t be dramatic,” he said. “Some of the things he suggested on the campaign trail -- reluctance to criticize Putin, the constant theme that we can have a better relationship with Russia --

I worry that we could be making a fairly major departure that in the end would end up endangering American interests.”

Israel

The president-elect has said he wants to help broker an Israeli-Palestinian peace deal and potentially make his son-in-law Jared Kushner the negotiator, but experts say the prospects of an agreement are slim to none.

“It has nothing to do with who the mediator is,” said the Wilson Center’s Miller, “and has a lot to do with the simple reality that Benjamin Netanyahu and Mahmoud Abbas are simply not prepared to take the kinds of decisions on the six core issues that drive the conflict -- borders, security, refugees, Jerusalem, recognition of Israel as the nation-state of the Jewish people, end of claims in conflict. Neither side is prepared to take the kind of decisions that would allow a mediator to get close.”

What could permanently undermine the peace process, Miller said, is a transfer by the Trump administration of the U.S. embassy in Israel from Tel Aviv to Jerusalem.