The Arab Spring gave way to bloodletting in Syria, a refugee exodus and surging jihadist violence. Obama gave way to Trump. The United Kingdom chose to Brexit. And for many around the world, while the 2010s began with hope for a more equitable world, they end with a slide towards nationalistic populism.
The following is a look at some of the people and events that shaped the past decade:
The United States will begin the 2020s with Donald Trump in the Oval Office, as a president of a country riven by political, societal and economic discord - and a leader facing impeachment.
Trump - who is accused of abusing his power to ask a foreign nation, Ukraine, to investigate a domestic political rival - has every chance of being acquitted by the Senate, where his Republican Party faithful hold the majority.
As the 2010s draw to a close, the booming success of the American economy will help his chances at re-election next year.
Abroad, Trump is rough with his allies, flouts international agreements and does not hesitate to boost his ties with authoritarian governments like that of North Korea's Kim Jong Un.
A disappointing Arab Spring
After the decade began with the hope of the Arab Spring, it ends with strongmen back in power in several countries.
On January 14, 2011, Tunisian dictator Zine El Abidine Ben Ali was chased from office by a popular rebellion that was unthinkable only a few weeks before.
The Arab Spring erupted in the Middle East and North Africa.
Libyan leader Muammar Gaddafi was toppled that same year in a NATO-backed uprising.
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In Egypt, the protests in Cairo's Tahrir Square spelled the end of Hosni Mubarak's reign, but the country ended the decade in the iron grip of general turned President Abdel Fattah al-Sisi.
The fate of millions of people would be changed in Syria. A protest movement against the ruling Assad family descended into a bloody crackdown and eventually a brutal civil war.
In eight years of conflict since early 2011, more than 370 000 people have been killed and millions have been displaced from their homes. And the conflict has gone global.
Russia intervened on behalf of Bashar al-Assad. Turkey moved to prevent the Kurds from setting up a stronghold on the border.
The West built a coalition to defeat the "caliphate" of the Islamic State (IS), an extremist group that profited from the chaos to claim swathes of territory in Syria and Iraq.
The jihadists wrought havoc, and attracted thousands of foreign fighters - mainly from Europe - to their cause.
Islamic State leader Abu Bakr al-Baghdadi proclaimed the establishment of the "caliphate" in June 2014, extending from Aleppo in northern Syria to Diyala in Iraq.
The organisation would eclipse Al-Qaeda and unleash a new torrent of violence, taking several forms.
It encouraged its followers to commit their own elementary acts of terror, rather than stage elaborate operations like the September 11 attacks.
France, Belgium, Denmark and Britain all fell victim to jihadist attacks in the course of the decade. The movement swept through Africa's vast Sahel region, and parts of Asia.
But the United States, their Kurdish allies and European nations together seized back the IS "caliphate" - which was declared eliminated in March this year.
And Baghdadi was killed in a raid by US special forces - he died "like a dog," as Trump said on October 27.
The Syrian conflict resulted in the export of violence, but also in an immense human tragedy on Europe's doorstep, as millions left their homes in search of security and a better life.
They criss-crossed Europe in giant processions, ending up in whichever country would welcome them with open arms. Chancellor Angela Merkel's Germany thought it could absorb the influx of refugees.
"If Europe fails on the question of refugees, if this close link with universal civil rights is broken, then it won't be the Europe we wished for," she said on August 31, 2015.
Hundreds of thousands of Syrians would end up in Germany.
In the north of France, at the port of Calais, migrants crammed into makeshift camps waiting for a chance to cross the English Channel to Britain.
In the Mediterranean, desperate migrants made the journey through north Africa to the sea, using rickety boats and rafts to try to get to Europe.
Many did not survive.
In the United States, Trump made the fight against migrants illegally entering the country from Mexico one of his signature political issues.
And he asked Congress for billions of dollars to build a wall to help keep them out.
Trump's rise emboldened a surging wave of populist and far-right political movements - from Hungary's Viktor Orban to Italy's Matteo Salvini and Brazil's Jair Bolsonaro.
In France, the far-right remained a political force thanks to the Le Pen family, and gathered strength in Germany, where some questioned the soundness of Merkel's open arms.
In Britain, a historic 2016 referendum in which voters opted to leave the European Union promised to change the complexion of the continent.
After a tortuous process, Prime Minister Boris Johnson seems on his way to leading the United Kingdom out of the bloc after an election win, with the blessing of Trump, the first US leader not to back European unity.
Citizens take action
As 2019 comes to an end, one Swedish teenager has rewritten the rules about activism and awakened public consciousness about the fight against climate change.
Millions of young people see themselves in 16-year-old Greta Thunberg, and think their elders have sacrificed the planet on the altar of economic growth and creature comforts.
"How dare you?" the teen said in September at the United Nations, challenging world leaders over their inaction on global warming.
Protection of the environment is front and centre in many countries. But a simpler question - how men and women relate to each other - also took centre stage during the 2010s.
The #MeToo movement, which went viral in the wake of a litany of allegations against Hollywood producer Harvey Weinstein, has encouraged women to confront their abusers, and led to the downfall of a number of powerful men.
The question of gender and identity also rose to the fore this decade, with many redefining what it is to be a man or a woman - or neither.
"They" - the pronoun preferred by many who identify as non-binary - was Merriam-Webster's word of the year in 2019.
US, China lock horns
On the back of skyrocketing growth, China became the world's number two economy in 2010, surpassing Japan and only trailing the United States.
In the middle of the decade, China staked a claim in the technology sector, working to become a world leader in robotics, information tech and clean energy.
Beijing is trying to change gears - it no longer is satisfied with being home to the factories that produce the world's consumer goods.
America has sensed that its supremacy could be contested. And under Trump, that concern erupted in the open.
The Republican leader launched a trade war with China, accusing it of rampant intellectual property theft.
"Trade wars are good and easy to win," Trump boasted in 2018.
He has unleashed stiff tariffs on Chinese goods, but Beijing did not blink.
And even if the two countries just signed a "phase one" trade deal, their arm wrestling is sure to define the next decade.