The biggest international stories of 2017: From North Korea and Yemen to ISIS and terrorism ABC News reporters around the world look back at 2017 -- and ahead to 2018.

 -- 2017 was a tumultuous year on the global stage as world leaders confronted a morphing U.S. role in international affairs and crises across the world.

President Donald Trump projected a policy of "America First" as he ceded the United States' leadership on climate change, blasted international agreements and demanded more of U.S. allies. The world banded together to fight climate change, while humanitarian crises unfolded in Yemen and Myanmar. ISIS was beat back in Syria and Iraq, but its followers unleashed attacks in Europe and across the world. Middle East machinations kept leaders busy, while the world looked ahead to next year's Winter Olympics in Pyeongchang, South Korea.

ABC News' team of reporters around the world has a look back at 2017, and a glimpse ahead at what stories will make news in 2018.

North Korea keeps tensions high

North Korea's provocations continued throughout 2017, followed by stronger international sanctions each time. The country test-fired various ranges of missiles repeatedly throughout the year, almost every few weeks during the first half of 2017. Its latest ICBM flew for 50 minutes and reached 2,800 miles in height in late November -- a milestone that could threaten the mainland United States once the North potentially masters the technology to top it with a nuclear warhead.

The assassination of the North Korean leader Kim Jong Un's half-brother, Kim Jong Nam, at an airport in Malaysia in February is thought to have been carried out by or on behalf of North Korean authorities and demonstrated the brutal nature of the regime. Otto Warmbier, an American college student held captive for allegedly stealing a propaganda paper, was released in June in a state of coma but later died soon after his return. Kim Jong Un was also rumored to have purged or executed numerous top officials throughout this year in order to consolidate his power.

The year also witnessed “war of words” between Kim and Trump. The U.S. leader threatened that North Korea will "be met with fire, fury, and frankly power," and called Kim the "Little Rocket Man.” The North responded by calling Trump "a mentally deranged American dotard.”

The North's nuclear weapons program is expected to pick up speed heading into 2018. While tensions have remained high, experts say once North Korea is confident that it holds the bargaining nuclear power, it could come to the negotiating table to gain assurance for the regime's survival.

-Joohee Cho, Seoul

U.S. global role morphs under Trump

Trump’s inauguration as U.S. president at the beginning of 2017 sent shockwaves across the world, with Trump promising to enact foreign policies that put "America First.”

Trump pulled the U.S. out of the Trans-Pacific Partnership and vowed to take the U.S. out of the Paris Climate Accord. He has demanded more of U.S. allies -- calling on South Korea and Japan to foot more of the bill for U.S. troops stationed there, for example. Commentators have debated whether Trump had passed at least part of the mantle of leadership to countries like China and Germany.

Trump frequently criticized the United Nations on the campaign trail, and at the U.N. General Assembly in September, he told other world leaders they should put their own countries’ interests first.

U.N. members were overwhelmingly united, though, in rebuking the United States this month, when members of the U.N. General Assembly world nations -- including a number of close U.S. allies -- voted to condemn Trump’s announcement that the U.S. would recognize Jerusalem as Israel’s capital and move the U.S. Embassy to Israel there.

Back at home, Trump faces calls to do more to combat what U.S. intelligence agencies have said is Russian meddling in the American electoral process. While reports have shown a concerted Russian effort to support Trump’s candidacy and oppose that of his Democratic opponent, Hillary Clinton, the Kremlin has denied interfering.

-Ben Gittleson, New York

China on the rise

2017 was a banner year for Chinese President Xi Jinping. Xi began the year standing before the world’s economic elite at the Davos economic forum giving a full-throated defense of globalization and ended it enshrined in the charter of the Chinese Communist Party, officially making him the most powerful Chinese leader since Mao Zedong. Only Mao didn’t command the world’s second-largest economy.

Meanwhile, Xi’s China has been forced into the fray as the de-facto defender of the Paris Climate Agreement and international trade as Trump extricated American leadership in those areas.

Despite numerous challenges at home, including find a feasible way to redirect China’s rapidly changing economy, expect Xi to keeping projecting China’s increasingly robust foreign policy across the globe in 2018 with an even more urgent confidence. The Chinese military opened its first overseas base and is being prepped to do more to defend Chinese interests abroad.

But there are already signs from some countries, like Australia and Pakistan, of pushback against Chinese influence. 2018 may be the year China receives the increased attention and scrutiny that comes with being a superpower.

-Karson Yiu, Hong Kong

Rohingya flee Myanmar ‘ethnic cleansing’

The ongoing exodus of the persecuted, officially stateless Rohingya Muslims from Myanmar became the world’s fastest-growing refugee crisis in 2017.

A series of attacks on Myanmar border troops precipitated a heavy-handed military crackdown that, according to Doctors Without Borders, killed 6,700 Rohingya in its first month. The Myanmar government claims only 400 were killed.

More than 600,000 Rohingya have crossed into Bangladesh since the violence broke out in Myanmar’s Rakhine state. The U.S. has called the attacks “ethnic cleansing.”

The crisis has tainted the legacy of Myanmar’s de-facto civilian leader Aung Sang Suu Kyi, a Nobel Laureate, for her silence on the issue.

The crisis will extend into 2018. Bangladesh announced in October that it is building the largest refugee camp in the world to house the over 800,000 Rohingya seeking asylum within its borders. The governments of Myanmar and Bangladesh have agreed to begin repatriating in early 2018 Rohingya who can prove their residence in Myanmar. But Myanmar has for decades refused to issue official identity documents to the Rohingya.

-Karson Yiu, Hong Kong

Yemen’s humanitarian catastrophe grows

Yemen is one of the largest humanitarian catastrophes in the world. Millions of Yemenis are in desperate need of aid, including some 8.4 million who are a step away from famine, according to the U.N., and severe acute malnutrition is threatening the lives of about 400,000 children. In 2017, Yemen became home to the world’s largest cholera outbreak, with about 1 million cases and more than 2,000 cholera-related deaths.

In November, the situation worsened when a Saudi-led military coalition that is fighting Iran-backed Houthi rebels blockaded Yemen’s ports. Since then, the blockade has been eased, but it has further limited access to food, fuel and medicine.

While the cholera outbreak has declined, aid workers now warn that a suspected outbreak of diphtheria, an infection that can be deadly, could quickly become an epidemic.

On Dec. 4, the war in Yemen took a surprising turn when ex-President Ali Abdullah Saleh was killed after he abandoned his Houthi allies for the Saudi-led coalition, which is backed by the U.S. and the United Kingdom.

Since then, violence has escalated in Yemen. The war could get even worse in 2018.

-Lena Masri, London

ISIS loses territory, but ‘lone wolves’ still a threat

Three years after the leader of ISIS declared a caliphate, an international coalition this year largely took back control of territory in Iraq and Syria where the group had imposed draconian rules on the local population.

After months of bloody, door-to-door fighting in Iraq’s second-largest city, Mosul, Iraqi forces this summer forced ISIS to retreat, and life there began to return to normal. The battle shifted to ISIS’s de facto capital in Raqqa, Syria, where an international coalition also beat back ISIS. Remnants of the group shifted to much-diminished territory in Syria, where the so-called caliphate was largely wiped out.

Throughout 2017, though, ISIS’s online propaganda inspired a multitude of supporters contemplate or carry out attacks in Europe, the U.S. and the Middle East. Militant groups across the world -- from Somalia and North Africa to Afghanistan and the Philippines, have pledged allegiance to the group and continue to carry out attacks. Intelligence officials across the world fear that ISIS’s territorial defeat may lead to more bloodshed in the future as “lone wolves” take up the group’s call to arms.

-Ben Gittleson, New York

Europe hit by wave of terror attacks

In 2017, Europe was hit by a number of terror attacks: a truck attack in Stockholm, the shooting of police officers at the Champs-Élysée boulevard in Paris, and twin vehicle attacks in Barcelona and Cambrils, Spain.

The U.K. was hit by five attacks, from the Ariana Grande concert bombing in Manchester to an attack on Muslim worshippers in London. At least nine plots have been thwarted in the past year in Great Britain alone, a spokesman for the British prime minister said this month.

As ISIS lost territory across Syria and Iraq in 2017, officials feared its remnants would inspire an increase in terror attacks elsewhere, particularly in Europe.

Across the continent, countries continue to worry about what a top British intelligence official in October called a threat that is “multi-dimensional, evolving rapidly and operating at a scale and pace we’ve not seen before.”

-Lena Masri, London

High temperatures, intense storms put focus on climate

Trump promised over the summer to pull the U.S. out of the Paris Climate Accord, ceding leadership on the fight against climate change to the rest of the world. After Syria and Nicaragua announced they would join the agreement, the U.S. became an outlier as nations teamed up to combat carbon pollution.

French President Emmanuel Macron announced his country would assert itself on the issue, giving “Make Our Planet Great Again” grants to climate scientists -- a play on Trump’s “Make America Great Again” campaign slogan. In November, nations gathered in Bonn, Germany, vowed to move forward with the 2015 Paris Accord. This month, China, the world’s top polluter, announced an ambitious plan to curb its emissions.

While there is no scientific consensus about whether climate change is behind the growing intensity of storms across the world -- including hurricanes that wreaked havoc on Caribbean countries and U.S. this year -- the storms have led to calls from island nations and others to prioritize addressing carbon pollution. And the U.N.’s weather and meteorological agency said 2017 was on track to be the hottest year on record, other than 2015 and 2016, which were affected by the El Nino phenomenon.

-Ben Gittleson, New York

Saudi-Iranian competition flares as conflict racks Middle East

In 2017, Saudi-Iranian competition over regional dominance reached new heights, bolstered by a more combative posture by Saudi Arabia’s crown prince -- most dramatically embodied in what appeared to be his forcing Lebanon’s prime minister to resign, before international negotiations allowed a return to the status quo.

Under Trump, the U.S. has pushed itself closer to Saudi Arabia and made combatting Iran a priority. Saudi Arabia, meanwhile, has led a coalition battling Houthi rebels in Yemen, where thousands have suffered from cholera and diphtheria. While ISIS was rolled back from almost all the territory it held in Iraq and Syria, Russia’s intervention in Syria successfully allowed the Assad regime to regain control over much of the territory -- though it continues to rely heavily on Iran-backed militias such as Lebanese Hezbollah.

Saudi-Iranian proxy wars do not seem set to cool down, and a flare-up of the conflict in the northern Syrian province of Idlib as well as a continued devastating regime siege of East Ghouta, close to Damascus, are expected.

-Rym Momtaz, London

Doping and security fears cast pall over Olympics

When the 2018 Winter Olympics open in Pyeongchang, South Korea, in February, looming over them will be two stories from 2017: Russian doping and the continuing confrontation between the United States and North Korea over its nuclear program.

Russian athletes will be competing under a neutral flag at the Winter Games after their country was banned over the continuing doping scandal. The reason for the ban was the same scheme that saw Russia partly barred from the Summer Olympics in Rio de Janeiro, Brazil: allegations of a vast state-sponsored cover-up of doping by its athletes, involving Russia’s sports ministry and even its FSB intelligence service.

Rattling some nerves as well will be the nuclear standoff with South Korea’s neighbor to the north. U.S. ambassador to the U.N. Nikki Haley recently caused a furor when she suggested the United States could avoid the Games over security fears. While the White House has since signaled otherwise and most experts expect the Olympics to be safe, there are worries the North could seek to interfere and South Korea has asked the U.S. to delay planned military drills until after the Olympics, hoping for calm.

-Patrick Reevell, Moscow