 -- The 45th President of the United States, Donald J. Trump, has inherited a number of daunting foreign policy challenges spanning the globe from the Middle East through East Asia.

Trump tweeted this morning that "THE WORK BEGINS!" yet many of his top foreign policy positions have yet to be confirmed by the Senate, including CIA Director and Secretary of State.

The White House website says Trump will execute an "American first foreign policy ... focused on American interests and American national security." The White House policy will center on "peace through strength," made possible in part, it says, by pursuing "the highest level of military readiness."

ABC News looked at seven of the most challenging foreign policy issues facing the new administration, and what President Trump said about each over the past several months.

The White House announced today that for this new commander-in-chief, defeating ISIS and eliminating the direct threat it poses to Americans at home and abroad will be the "highest priority."

Just in the last two days, the United States military conducted two separate rounds of airstrikes in Libya and Syria its says killed nearly 200 ISIS and al-Qaeda militants. The U.S. Department of State has a standing "worldwide travel caution" for all Americans traveling abroad, which warns about the continuing threat of terror attacks.

"In the past year, major terrorist attacks occurred in Belgium, France, Germany, Turkey, Egypt, Saudi Arabia, Somalia, Nigeria, Syria, Iraq, Indonesia, Pakistan, Afghanistan, and Bangladesh among others," the State Department warning says. "Authorities believe there is a continued likelihood of attacks against U.S., Western, and coalition partner interests throughout the world, especially in the Middle East, North Africa, Europe, and Asia."

The new administration will be under enormous pressure to finish the fights to retake ISIS strongholds in Mosul, Iraq, and Raqqa, Syria -- and could easily be faced with a shift in enemy tactics, an insurgency and a protracted fight that could force the White House to make difficult decisions about whether to commit more U.S. forces on the ground.

Guiding stable government institutions to fill the vacuum left by ISIS and encouraging a successful political resolution to the five-year civil war in Syria, ideally including the removal of brutal Syrian dictator Bashar al-Assad, are also enormous challenges.

The refugee crisis caused by both the war in Syria and the violent tactics of ISIS is another pressing issue. Amnesty International estimates the conflict in Syria has forced more than 4.5 million refugees from Syria who are now living in Turkey, Lebanon, Jordan, Iraq and Egypt. The Trump administration will need to work with world powers to manage that refugee flow to prevent more humanitarian suffering and potential they have to destabilize governments that take them in.

What Trump has said: Trump has not presented a clear strategy to defeat ISIS, often claiming that public strategy discussion would tip off the enemy. He has said, though, that he would fight ISIS aggressively.

Yesterday, White House Press Secretary Sean Spicer announced that the Trump administration would be keeping the State Department's top counter-ISIS planner, Brett McGurk, to ensure continuity.

But in regards to the refugee crisis, Trump rejected calls from former Democratic presidential nominee Hillary Clinton to increase the number of refugees from Syria and Iraq admitted into the U.S. He instead proposed banning Muslim immigration to the U.S. and later called for "extreme vetting" of applicants.

2. RUSSIA

Unprecedented Russian hacking into the Democratic National Committee also highlights the enormous security threat posed to critical components of the U.S. government, infrastructure, defense technology and many other government operations that rely heavily on cybertechnology.

On it's website, Trump's White House announced it "will make it a priority to develop defensive and offensive cyber capabilities at our U.S. Cyber Command, and recruit the best and brightest Americans to serve in this crucial area."

Russia's military intervention inside Syria has effectively set up a proxy war with the U.S. and the rebel forces it backs. The U.S. has blamed Russia for its subsequent breakdown of cease-fire negotiations and the devastating siege of Aleppo, Syria.

On Monday, the Russians will hold peace talks in Astana, Kazakhstan. It's unclear if anyone from the Trump administration will attend.

And finally, Putin's war in Ukraine and illegal annexation of Crimea has sparked fears that he's seeking to reclaim Soviet-era borders and eventually could bait the NATO alliance into a military conflict.

What Trump has said:

Trump's recent comments on Russia have so far defied the conventional wisdom of either party and have drawn criticism from both sides.

Trump has not condemned the Russian hacks into the U.S. election process and has said he "would be looking at" the possibility of lifting sanctions against Russia tied to its illegal military annexation of Crimea, which the U.S. government has refused to accept.

He publicly doubted the intelligence community's assessment that Russia hacked the DNC, compared them to Nazis and blamed them for leaking false information about his ties to Russia.

Rather than stand against a potential revival of Soviet expansionism, critics say Trump seems to be embracing it. He has described the North Atlantic Treaty Organization (NATO) -- considered the first line of defense against Russian expansionism -- as "obsolete," while also suggesting he may not honor the organization's most sacred covenant of mutual defense.

During his confirmation hearing Trump's pick for secretary of state, former Exxon Mobile Chief Rex Tillerson, was questioned about his ties to Russia, where he did deals with the state-run oil industry and developed a personal relationship with President Vladimir Putin. Tillerson denied lobbying against Russian sanctions brought on by its aggression in Ukraine and said that sanctions are a "powerful tool."

In addition to saying the U.S. would benefit from a friendlier relationship with Putin, Trump has also praised him on Twitter recently, calling him "very smart" for deciding not to retaliate when President Obama kicked out Russian intelligence offers in response to the election hack.

3. NORTH KOREA

The United States is now more concerned than ever that North Korea is closer to its goal of miniaturizing a nuclear weapon that can be placed on long-range missiles, a move that could destabilize the region and the world. Just this week a South Korean news agency reported the North Koreans announced they're preparing to test mobile-launched ICMB's, but U.S. intelligence officials would not confirm those reports.

Unlike with Iran, the U.S. has not been able to negotiate an agreement on nuclear issues. The U.S. and North Korea have virtually no diplomatic relations and China is considered the only global power with any leverage over the regime.

Considering that three of North Korea's five nuclear tests have occurred during the rule of Kim Jong-un, it's clear the dictator is undeterred by the suffocating economic sanctions imposed by foreign nations. Though China's Foreign Ministry has criticized the North Korean test and urged international dialogue, recent tensions between the United States and China over the South China Sea could suppress Chinese support for taking a more aggressive approach to the North Korean regime.

What Trump has said: In response to North Korea's latest nuclear test, Trump's spokesman Kellyanne Conway said that if Trump is elected, North Korea will know the Americans "aren't messing around."

In January, after the North said it was close to being able to firing off a nuclear weapons that could reach the United States, Trump tweeted "It won't happen," which has been interpreted as a possible "red line" for the Trump administration.

In May Trump said he would be open to the idea of allowing North Korea's neighbors, including U.S. allies South Korea and Japan, to acquire their own nuclear arsenals -- a move that would effectively nuclearize the entire region and negate the cost and justification for stationing U.S. troops in the region.

"We cannot afford to be the military and the police for the world," he said at the time.

4. CLIMATE CHANGE

One year ago, nearly 200 nations signed a global pact, the Paris Agreement, to combat climate change with the shared goal of preventing global temperatures from rising more than 3.6 degrees Fahrenheit. The U.S., along with other developed countries, will have to make good on commitments to fund new low-carbon emissions systems in countries that are complaining that the finances are not coming as promised.

But the challenges on the road to achieving this shared goal are vast -- and they begin with the United States. Already, legal cases in the U.S. Supreme Court have stalled President Obama's plan to phase out coal power plants as part of his "Clean Power Plan." The delay could take years as the cases brought by various states play out.

Meeting the goals outlined in the Paris climate agreement will take significant effort both domestically and abroad.

Trump's pick to be the head of the Environment Protection Agency (EPA), Scott Pruitt, said during his nomination hearing he did not believe climate change is a "hoax" as Trump has previously claimed, but said he was in favor of rolling back environmental regulations he claims have hurt American industries.

What Trump has said: In May of this year, Donald Trump said he would "cancel" U.S. participation in the Paris Agreement.

"Any regulation that's outdated, unnecessary, bad for workers or contrary to the national interest will be scrapped and scrapped completely," Trump said. "We're going to do all this while taking proper regard for rational environmental concerns."

As mentioned, Trump has also tweeted that global warming is a "hoax" perpetrated by the Chinese.

While Tillerson has acknowledged climate change is a problem, ExxonMobil came under fire at its shareholders' meeting last year for rejecting resolutions that would have pushed the company’s resources toward renewable energy, according to the Washington Post.

5. TURKEY

Turkey, a NATO ally, is also accusing the United States of harboring a person that its leaders say is the equivalent of what Osama bin Laden was to the U.S. That was how the Turkish Minister of Justice described Fethullah Gulen, the cleric living in Pennsylvania and the man Turkey's government blames for inciting that failed coup this past summer. Turkey is insisting Gulen be extradited to Turkey, but the U.S. Justice Department has suggested Turkey has failed to present sufficient evidence of wrongdoing.

The Gulen movement is designated as a terrorist organization inside Turkey and Turkish President Recep Erdogan has been using the failed coup as an excuse to purge all his opposition. Disturbing accusations of imprisoning teachers and journalists and committing torture threaten the state's democracy have forced the U.S. to distance itself from the country, which has been a critical ally in the past. The tensions have created a pathway for Turkey to form partnerships with adversaries of the U.S.

Meanwhile, the U.S. relies on Turkish border control, Turkish armed forces and its military base in the fight against ISIS. A diplomatic rift with Turkey could damage U.S. efforts, though both Turkey and the U.S. have insisted they don't want that to happen.

What Trump has said: In a campaign interview with The New York Times last July, Trump applauded the Turkish president and the Turkish people for suppressing the failed coup attempt. He also said he thinks "Turkey can do a lot against ISIS, and I would hope that if I’m dealing with them, they will do much more about ISIS."

Asked about Erdogan jailing tens of thousands of people and Turkey's problems with civil liberties, Trump said, "I think it’s very hard for us to get involved in other countries when we don’t know what we are doing and we can’t see straight in our own country."

6. CHINA

Second, Trump has already taken the provocative step of questioning America's One China policy, which recognizes the island of Taiwan as a part of China. After winning the election, then President-elect held an unprecedented phone call with the Taiwanese President Tsai Ing-wen, which he says was initiated by Taiwan, that prompted the Obama administration to reaffirm its stance. U.S. policy does allow, however, for the sale of weapons to Taiwan, which it could use in a potential military conflict with the mainland.

And Third, Trump will need to decide how to confront China's militarization of disputed islands in the South China sea and its claim to Island in the East China Sea. Tillerson has said China's military actions are illegal, likening them to the taking of Crimea by Ukraine, and said the U.S. should send a signal that their action are "not going to be allowed."

Chinese state media responded by saying the Trump administration risks "large-scale war" if it attempts to intervene.

IRAN

For instance, if the U.S. were to accuse Iran of violating the deal, sanctions could snap back into place and the deal could fall apart. If Trump is unable to negotiate a new deal, Iran would likely return to making a nuclear weapons, which even President Obama drew as a red line. Without a nuclear deal, Trump would have no option other than military force to dismantle Iran's nuclear program.