But when it comes to tackling long-term global challenges such as climate change, poverty or peacemaking, it's also vital to identify which leaders are likely to stick around.
Whether democrats, dictators or somewhere in between, they're all balanced atop a shifting ziggurat of potential rivals. And only those with the home front under control are in a position to make meaningful promises for the 2020s or beyond. That's why France's Emmanuel Macron can map out a seven-year programme for reforming the European Union while Theresa May can't look beyond the date of Britain's exit from the bloc next year.
So for an alternative take on who really matters in global affairs, we picked 16 countries and analysed how long their leaders might hold off the palace coups, election defeats or waning powers that end political careers.
We've ranked them on their domestic muscle to see whether they are likely to be shaping events, or shaped by them.
Mohammed Bin Salman, Saudi Arabia
Crown Prince Mohammed bin Salman isn't king yet but he's already effectively running Saudi Arabia at the age of 32 and he could conceivably govern for another half century -- his father, King Salman, is 82, and former King Abdullah died at 90.
Even sceptics say that the prince has cleverly outmanoeuvred competitors, positioning himself to rule the absolute monarchy for decades by pushing aside other royals, though he has made enemies along the way.
"If he remains healthy and the politics, culture, society and economics of the country and the region go in a way that would support a long-term ruler, he could be in leadership for 50-plus years," said Paul Sullivan, a Middle East specialist at Georgetown University in Washington. "This is very rare."
Kim Jong Un, North Korea
A coup, assassination or war with the US appear to be the main risks to Kim Jong Un. But if none of them topple him, he will probably maintain his iron grip on North Korea for decades, just as his father and grandfather did.
Kim is believed to be in his thirties, so his natural lifespan could easily stretch for another forty or fifty years. Though his weight issues add an element of risk, his father, Kim Jong Il, died at 70, while his grandfather, Kim Il Sung, lived to be 82.
"I do not see any likely scenario in the near future that would undermine Kim Jong Un's power," said Sebastian Maslow, an assistant professor at Kobe University. "Unless we witness action by US or South Korean special military units to remove him by force, we will have to deal with Kim Jong Un as North Korean leader for some time to come."
Xi Jinping, China
After the Chinese Communist Party's move to repeal presidential term limits in February, the main question is how long will President Xi Jinping stay.
The constitutional provision barring heads of state from more than two consecutive terms was the only formal barrier keeping Xi, 64, from staying on past 2023. After being elevated to the same status as Mao Zedong in October, when his name was written into the Communist Party charter, he's positioned to influence China for decades to come.
"Xi has set out his ambition to lead China for the long-term, at least through the 2020s, I think we can assume, if he remains healthy," said Tom Rafferty, the Economist Intelligence Unit's regional manager for China. "Event risk still pertains, however. A bout of economic instability or a mishandled international confrontation -- neither of which can be discounted -- would weaken his position internally and give an opportunity to others."
Vladimir Putin, Russia
Over his 18-year rule, President Vladimir Putin has methodically neutralised any threat to his power, from ambitious oligarchs to Chechen separatists to Western sanctions.
But in 2024 a constitutional limit should force him to give up the presidency. He's already sidestepped those rules once, and he's suggested that's not something he'd do again. The challenge is to ensure his system and his inner circle are safe after he goes.
"Putin wants to keep the levers of influence to give him a veto over his successor's decisions," said Tatiana Stanovaya, a political analyst at the R Politik think-tank. "He has to build a system that will maintain the status quo even when he isn't president -- the Putin regime must remain even without Putin."
Recep Tayyip Erdogan, Turkey
Recep Tayyip Erdogan could become even more influential if he's reelected in November 2019, when more power will be concentrated in the Turkish presidency.
Prime minister from 2003 to 2014 before becoming the country's first directly elected president, the 64-year-old Erdogan survived a coup attempt in 2016 and enjoys strong support from voters as well as the backing of a nationalist opposition party. Although Erdogan is theoretically limited to two five-year terms, he can stretch that if a snap election is called during his second term.
A New York trial last year over the role of some Turkish nationals in an alleged multi-billion dollar conspiracy to undermine U.S. sanctions on Iran has fed the narrative of western conspiracy against Turkey and allowed Erdogan to tighten his grip on power.
"Erdogan is forming political alliances and overhauling laws to get elected as the first executive president," Nihat Ali Ozcan, an analyst at the Ankara-based Economic Policy Research Foundation of Turkey, said. "If he wins, Erdogan could possibly stay in power at least another decade."
Narendra Modi, India
Prime Minister Narendra Modi dominates India's political landscape. Although he lacks the upper-house majority necessary for big structural reforms, PM Modi's Bharatiya Janata Party has proven its popularity, winning numerous state-level elections since he came to power in 2014.
Regional rivals are vulnerable to the BJP's formidable election machine. "Certainly, it seems like they will come back into power in 2019 given their success in state elections and massive popularity -- and in 2024, that's also on the agenda," said Reshmi Khurana, a Singapore-based managing director at the consultancy Kroll. "The absence of a strong opposition makes that highly possible."
Ali Khamenei, Iran
Supreme Leader Ayatollah Ali Khamenei, who was initially elected president of the nascent republic in 1981, has survived an assassination attempt, frontline combat and prostate surgery. Backed by the Iranian Revolutionary Guard Corps and many religious and working-class Iranians, the 78-year-old hardliner is likely to be in power until he dies.
That could mean about another nine years, according to actuarial calculations by Scott Kush of the Life Expectancy Group in Menlo Park, California.
"One doesn't ascend to the pinnacle of power from the position of a virtual underdog in Iran's cutthroat politics without having canny Machiavellian skills," Ali Vaez, director of the Iran Project at the International Crisis Group said. "No one could pose a serious challenge to him."
Emmanuel Macron, France
The French electoral system has been kind to President Emmanuel Macron, enabling him to turn 24 percent of the vote in last April's first round into total dominance of France's executive and legislative branches as the country's traditional parties imploded.
Fixed five-year terms for both the head of state and the National Assembly mean he shouldn't have to face a national vote until 2022.
Forty-year-old Macron's popularity took a beating in his first months in office as he pushed through policies that were seen as benefiting the wealthy but he recovered toward the end of the year. If unpopular measures such as abolishing the wealth tax and liberalizing labor laws can bring economic growth and jobs, the president may well repeat his winning combination in 2022.
"The left-right split hasn't disappeared," said Jerome Fourquet, the head of Ifop's opinion surveys. "But the emergence of a vast central block means that those who embody that split are for the moment condemned to being minority parties."
President Nicolas Maduro faces newfound challenges with an election set for May and ruinous inflation and hunger prompting months of bloody street protests last year. Yet the 55-year-old former bus driver still has the support of the military and could extend two decades of sweeping victories for his socialist party with the opposition demoralized and divided.
Maduro has increased government spending in recent months, started the process of rewriting the constitution and ramped up the arrests of high-ranking oil industry executives-sidelining potential Chavista rivals-as he seeks to secure his own six-year mandate.
"Maduro governs with an instability fueled by the economic crisis," said Edgar Gutierrez, a political analyst in Caracas. "If the opposition manages to unite and just voting conditions are achieved, then there could be political change. If not, Maduro could remain."
Donald Trump, US
US President Donald Trump's first year in office has seen surging markets and the lowest unemployment in 17 years. But that's still to translate into support for the president.
Trump, 71, has the lowest approval rating of any modern US leader over his first 14 months. The last two presidents to fight a campaign with such poor poll numbers were George HW Bush and Jimmy Carter. Both were defeated.
Still, the special counsel investigation into possible ties with Russia is unlikely to cut short his term. Removing Trump from office by impeachment would need a two-thirds majority in the Senate, a distant goal even if the Democrats were to win back control in November.
"A lot of people have been speculating this is the end -- for a year and a half," said Jennifer Lawless, a professor of government at American University in Washington. "It's unlikely that anything would happen."
Muhammadu Buhari, Nigeria
Muhammadu Buhari is likely to retain his grip on Nigeria's presidency until at least the end of his current term in 2019, so long as his health holds out.
The former military ruler spent more than five months in London last year undergoing treatment for an undisclosed ailment, but has displayed renewed vigor since returning home in August.
While 75-year-old Buhari made some headway against an Islamist insurgency, he's struggled to improve living standards in the oil-dependent economy. Though he would start as favorite for reelection given his overwhelming popularity in the north, he'll need to rebuild the coalition that secured him victory last time around.
"He stands more than a fair chance," said Robert Besseling, executive director of political risk advisory firm EXX Africa. "It's not going to be plain sailing though."
Benjamin Netanyahu, Israel
Benjamin Netanyahu's scandals have gripped Israel for a year. But the country's longest-serving prime minister since founding father David Ben-Gurion held his fractious coalition together all the same.
His partners aren't rushing to bring down a nationalist government that's given in to ultra-Orthodox demands, while efforts to rush through a budget suggest there's little appetite for elections before they're due.
If the 68-year-old Netanyahu survives the police investigations, he could win another four-year term in 2019 and he might even be around for longer, said Avraham Diskin, professor emeritus of political science at the Hebrew University of Jerusalem. That could all change if Netanyahu is indicted, though, and several politicians have begun to prepare for the post-Netanyahu era.
"Some people are starting to write him off but I don't think it's time for that just yet," Diskin said.
Shinzo Abe, Japan
Until a few weeks ago, Abe looked like a sure bet to win a party leadership election in September that would clear the way for him to become Japan's longest-serving prime minister. Yet a land-deal scandal has dented his chances. The 63-year-old has denied ordering officials to tamper with documents, but even his allies are starting to turn on him. One thing going in his favor: He faces scant competition within the ruling Liberal Democratic Party.
Already in office for a total of about six years, Abe could yet choose to step down before the end of his term, for example, if he succeeds in his goal of revising the pacifist constitution to incorporate a reference to the Self-Defense Forces.
"I think he will serve another term as party leader, but I think it will be his last," said Steven Reed, a professor of political science at Chuo University in Tokyo.
Angela Merkel, Germany
Angela Merkel, 63, is settling down for another four years as German chancellor, but she looks more vulnerable than ever before. While few would count her out even after 12 years in power, a much-criticized coalition deal, restive younger leaders and signs that voters want fresh faces in charge present a growing challenge.
A popular backlash against Merkel's open-borders refugee policy and an inconclusive national election in September forced her Christian Democratic bloc to seek support from the Social Democrats again, an alliance symbolizing the political center.
While there's still speculation that Merkel could leave midway through a fourth term and she's in the twilight of her chancellorship, she's defied expectations before and hasn't anointed a successor.
"There will be more young, promising people in her party that challenge her, and then she will realize her time is over," said Andrea Roemmele, a professor at the Hertie School of Governance in Berlin. "I'm quite confident that she won't run another time."
Theresa May, UK
U.K. Prime Minister Theresa May could be gone by the end of the month or she could limp on to see Brexit over the finish line in March 2019. Few of her lawmakers think she will still be in office come the next scheduled election in 2022.
"She is very vulnerable," said Nick Anstead, a lecturer in political communication at the London School of Economics. "Her greatest strength is that there is no obvious candidate to replace her who could unite the Conservative Party."
Michel Temer, Brazil
Michel Temer is the oldest and least popular president since Brazil's return to democracy in 1985. He will probably also be the briefest.
Elections are due in October and 77-year-old Temer has repeatedly said he won't be running. Though the economy is gradually recovering from the worst recession on record, most Brazilians aren't feeling much improvement yet and Temer has been pushing a series of unpopular austerity measures including a liberalization of labor laws and a cut in pension benefits. "There's been significant progress on the economic front under the Temer government and that has helped confidence to recover," said Camila Abdelmalack, an economist at CM Capital Markets in Sao Paulo.
In December even Temer himself joked about his approval ratings, saying that his government's support had doubled-to a whopping 6 percent. Even if he rides out the rest of his term, he'll have been in office for only two years and five months, less even than Fernando Collor, who was toppled by impeachment.
That's the consensus for now. But as Xi Jinping showed last month, even long-term prospects can change quickly when a serious player makes their move. We'll be watching carefully for more events that could reshape the outlook.