Here's a guide to a year of conflict and discord, through the words of some of the world's leaders.
Greek Prime Minister Alexis Tsipras: "We have a great opportunity for a new beginning."
The leftist Greek politician's Syriza party won landmark elections in January. Tsipras preached a new way forward for Greece after years of crippling austerity and compounding debt. But a failure to reach an accord with European Union authorities in Brussels has led to a return to the grinding status quo, which saw Tsipras contest and once more win elections in September, though with a humbler mandate.
French President François Hollande: "France is at war."
That's what France's president declared in the hours after the terrorist attacks in Paris on Nov. 13. The coordinated strikes by militants linked to the Islamic State group killed 130 people. France bolstered its efforts in hitting Islamic State targets in the Middle East and attempted to forge a grand coalition against the group. In the United States, meanwhile, the Paris attacks cast a long shadow, with Republican politicians, in particular, invoking the threat of Islamist infiltration to curb arrivals of refugees and Muslim immigrants.
Syrian President Bashar al-Assad: "Wrong [policies] adopted by Western states, particularly France, toward events in the region and its ignorance of the support of a number of its allies to terrorists are reasons behind the expansion of terrorism."
The embattled Syrian leader seized upon the French tragedy to make his case that countries that backed his opponents — which include some militant factions — had made a huge mistake. France had long been calling for Assad's ouster, and now one of his foes — the Islamic State — had struck one of Europe's most hallowed centers. But Assad's opportunistic statements came even as his regime continued to pound civilian areas in Syria, causing untold death and destruction. Its actions have spurred an epic humanitarian crisis that has seen roughly half the country's population fleeing their homes and more than 4 million Syrians leave the country. As the year drew to a close, the U.N. Security Council reached an important agreement on a peace process to end the Syrian conflict, but it said little about Assad's departure.
German Chancellor Angela Merkel: "We will cope."
Time magazine named the German leader its "person of the year" in 2015 in part because of her outspoken defense of desperate refugees, tens of thousands of whom arrived at Europe's borders in a massive influx this year. Her summertime declaration that Germany could accommodate up to a million refugees and her repeated rhetoric about the West's responsibility to those fleeing war won her the respect of many overseas. But Merkel's stance is not popular at home and even led to a backlash from within her ruling center-right party.
Hungarian Prime Minister Viktor Orban: "The people who are coming here grew up in a different religion and represent a completely different culture."
The European leader perhaps most vocal in his opposition to welcoming refugees was the head of a nation situated along the route to Germany. Under Orban's right-wing government, Hungary built a fence along its border with Serbia to obstruct the flow of migrants making the trek from Greece and countries farther south and east. Orban cast the refugees — the vast majority of whom had no desire to remain in Hungary — as a civilizational threat and styled himself as a kind of defender of Christendom.
President Obama: "Let’s not forget that freedom is more powerful than fear."
In the wake of the Paris attacks, the U.S. president reiterated his administration's commitment to the fight against the Islamic State. But Obama also insisted that dealing with security threats would not mean "abandoning our values." It was a gesture to the rather heated American conversation, fueled by statements from Republican presidential candidates grandstanding about the dangers of radical Islam, calling for a halt to arrivals of Syrian refugees and even suggesting that all Muslims be stopped from coming to the United States.
British Prime Minister David Cameron: "You ain't no Muslim, bruv."
The British leader echoed the words of a bystander-turned-viral-video-star who filmed himself berating a suspected Islamist militant after a foiled attack on London's Underground. Despite calls for tolerance and calm from Western leaders, attitudes toward Muslims have hardened in Europe and the United States.
Iranian President Hassan Rouhani: "A new chapter has started in Iran's relations with the world."
So said Iran's president during his address to the U.N. General Assembly in September. He was heralding the accord forged in July between Iran and world powers over Tehran's nuclear program. The deal with Iran was hailed as a landmark piece of diplomacy, the result of many rounds of negotiations. As Iran complies to strict limits on its nuclear capacity under the terms of the agreement, it will receive relief from stifling international sanctions.
Israeli Prime Minister Benjamin Netanyahu: "What a stunning, historic mistake!"
Not all world leaders were impressed with the Iran deal, though. The most outraged figure was Israeli Prime Minister Benjamin Netanyahu, who had campaigned for months against this opening to Iran's regime — one that he cast in the same light as the murderous Islamic State. The day after the accord was announced in July, Netanyahu deemed it a "historic mistake." He doubled down on his angry rhetoric a few months later at the U.N. General Assembly and glared in an awkward moment of silence at the seated dignitaries before him. But neither his efforts, nor those of Republicans and neoconservatives in Washington, could scupper the enterprise.
Russian President Vladimir Putin: "Allah decided to punish the ruling clique in Turkey by stripping it of its sanity."
One of the more dangerous geopolitical flare-ups in 2015 took place in the wake of the Russian intervention in Syria on behalf of the embattled Assad regime. Turkey, deeply unhappy with the Kremlin's power play, brought down a Russian jet that had strayed into Turkish airspace. This precipitated a war of words between Moscow and Ankara and soured ties between the two historical regional powerbrokers.
Turkish President Recep Tayyip Erdogan: "I will not remain in this post."
Putin's Turkish counterpart reacted angrily to Russian suggestions that his government was abetting the Islamic State's illicit smuggling activities across the border in Syria and Iraq. Erdogan vowed that he would resign if the Russian allegations were proven true. It was an ironic declaration by the Turkish president, who had otherwise spent much of the year consolidating his grip on power.
The ruling Justice and Development Party, a center-right religious nationalist party Erdogan co-founded, lost its parliamentary majority in June elections. It was seen as a blow to Erdogan, who currently occupies what is supposed to be a ceremonial post and had hoped for a strong electoral mandate that would guarantee him greater executive powers. Undeterred, he pushed for new elections in November, which his party won handily — thus cementing his place as the most significant leader in the history of the Turkish republic since its founder, Mustafa Kemal Ataturk.
Japanese Prime Minister Shinzo Abe: "I express my feelings of profound grief and my eternal, sincere condolences."
To mark the 70th anniversary of the end of World War II, Japan's nationalist leader delivered a much-anticipated speech on his country's controversial role in the epochal conflict. He stopped short of a formal apology, though, much to the ire of China. The spats over history between Beijing and Tokyo underpin more immediate tensions in the region, where many nations are warily eyeing China's expansionist behavior in the South China Sea and elsewhere.
Indian Prime Minister Narendra Modi: "The country has to stay united."
Attacks by Hindu nationalists on Muslims over allegations of beef consumption — many Hindus consider cows as sacred and eating beef as taboo — dominated news in India. Many are worried about a growing climate of intolerance and intimidation of minorities stoked by the advent of the conservative government led by Modi, a Hindu nationalist. Modi eventually broke his conspicuous silence on the matter and urged all Indians to rally together and combat poverty, not one another.
Zimbabwean President Robert Mugabe: "Cecil the lion was yours, and you failed to protect him."
Zimbabwe's nonagenarian president upbraided his people (and others) after news of the illegal killing of a famed lion by an American hunter. Sadly more than most stories out of Africa, the death of Cecil the lion earned global headlines and outrage. Mugabe's rambling remarks did little to boost conservation efforts.
Canadian Prime Minister Justin Trudeau: "Because it's 2015!"
The sweeping victory of Canada's Liberal Party in federal elections in October catapulted the youthful Justin Trudeau into the country's top post. The cabinet he unveiled upon his inauguration was notably diverse — 15 out of 30 senior ministers are women. When asked by a reporter to explain the rationale behind the composition of his cabinet, Trudeau offered this simple retort, which drew cheers far beyond Canada.