By ANGELA CHARLTON and THOMAS ADAMSON

PARIS (AP) — More than a million people surged through the boulevards of Paris behind dozens of world leaders walking arm-in-arm Sunday in a rally for unity described as the largest demonstration in French history. Millions more marched around the country and the world to repudiate three days of terror that killed 17 people and changed France.

Amid intense security and with throngs rivaling those that followed the liberation of Paris from the Nazis, the city became “the capital of the world” for a day, on a planet increasingly vulnerable to such cruelty.

More than 40 world leaders headed the somber procession — Israeli Prime Minister Benjamin Netanyahu and Palestinian President Mahmoud Abbas; Ukrainian President Petro Poroshenko and Russian Foreign Minister Sergey Lavrov — setting aside their differences with a common rallying cry: We stand together against barbarity, and we are all Charlie.

At least 1.2 million to 1.6 million people streamed slowly through the streets behind them and across France to mourn the victims of deadly attacks on the satirical newspaper Charlie Hebdo, a kosher supermarket and police officers — violence that tore deep into the nation’s sense of security in a way some compared to Sept. 11 in the United States.

“Our entire country will rise up toward something better,” French President Francois Hollande said.

Details of the attacks continued to emerge, with new video showing one of the gunmen pledging allegiance to the Islamic State group and detailing how the attacks were going to unfold. That gunman, Amedy Coulibaly, was also linked to a new shooting, two days after he and the brothers behind the Charlie Hebdo massacre were killed in nearly simultaneous police raids.

The attacks tested France’s proud commitment to its liberties, which authorities may now curtail to ensure greater security. Marchers recognized this as a watershed moment.

“It’s a different world today,” said Michel Thiebault, 70.

Illustrating his point, there were cheers Sunday for police vans that wove through the crowds — a rare sight at the many demonstrations that the French have staged throughout their rebellious history, when protesters and police are often at odds.

Many shed the aloof attitude Parisians are famous for, helping strangers with directions, cheering and crying together. Sad and angry but fiercely defending their freedom of expression, the marchers honored the dead and brandished pens or flags of other nations.

Giant rallies were held throughout France and major cities around the world, including London, Madrid and New York — all attacked by al-Qaida-linked extremists — as well as Cairo, Sydney, Stockholm, Tokyo and elsewhere.

In Paris, the Interior Ministry said “the size of this unprecedented demonstration makes it impossible to provide a specific count,” noting that the crowds were too big to fit on the official march route and spread to other streets.

Later, the ministry said 3.7 million marched throughout France, including roughly between 1.2 million and 1.6 million in Paris — but added that a precise count is impossible given the enormity of the turnout.

“I hope that at the end of the day everyone is united. Everyone — Muslims, Jews, Christians, Buddhists,” said marcher Zakaria Moumni. “We are humans first of all, and nobody deserves to be murdered like that. Nobody.”

On Republic Square, deafening applause rang out as the world leaders walked past, amid tight security and an atmosphere of togetherness amid adversity. Families of the victims, holding each other for support, marched in the front along with the leaders and with journalists working for the Charlie Hebdo newspaper. Several wept openly.

“Je Suis Charlie” — “I Am Charlie,” read legions of posters and banners. Many waved editorial cartoons, the French tricolor and other national flags.

As night fell on the unusually unified city, some lit candles.

“It’s important to be here for freedom for tolerance and for all the victims. It’s sad we had to get to this point for people to react against intolerance, racism and fascism,” said Caroline Van Ruymbeke, 32.

The French president joined Netanyahu in a visit to a synagogue Sunday night as authorities sought to reassure the Jewish population — Europe’s largest — that it is safe to stay in France. About 7,000 of France’s half-million Jews emigrated to Israel last year amid concerns for their safety and the economy.

“The entire world is under attack” from radical Islam, Netanyahu said, citing attacks in cities from Madrid to Mumbai. He said these aren’t isolated incidents but part of a “network of hatred” by radical groups.

At the synagogue, 17 candles were lit in tribute to the victims of the attacks. One was lit by a hostage at the kosher grocery store. The last was lit by two women whose sons were killed by Mohamed Merah, a radical Islamic gunman who attacked a Jewish school and paratroopers in southern France in 2012.

The U.S. was represented at the Paris rally by Ambassador Jane Hartley. At an international conference in India, U.S. Secretary of State John Kerry said the world stood with the people of France “not just in anger and in outrage, but in solidarity and commitment to the cause of confronting extremism and in the cause that extremists fear so much and that has always united our countries: freedom.”

The three days of terror began Wednesday when brothers Said and Cherif Kouachi stormed the Charlie Hebdo newsroom, killing 12 people, including two police officers. Al-Qaida’s branch in Yemen said it directed the attack to avenge the honor of the Prophet Muhammad, a frequent target of the weekly’s barbs. Charlie Hebdo assailed Christianity, Judaism as well as officialdom of all stripes with its brand of sometimes crude satire.

On Thursday, police said Coulibaly killed a policewoman. The next day, he seized hostages at the kosher market while the Kouachi brothers were holed up at a printing plant near Charles de Gaulle airport. It ended at dusk Friday with raids that left all three gunmen dead. Four hostages at the market were also killed.

Five people held in connection with the attacks were freed late Saturday, leaving no one in custody, according to the Paris prosecutor’s office. Coulibaly’s widow, last seen near the Turkish-Syrian border, is still being sought.

France remains on high alert while investigators determine whether the attackers were part of a larger extremist network. More than 5,500 police and soldiers were deployed Sunday across France, guarding marches, synagogues, mosques, schools and other sites.

“The terrorists want two things: they want to scare us and they want to divide us,” Foreign Minister Laurent Fabius told TV channel iTele. “We must do the opposite: We must stand up and we must stay united.”