The outpouring of solidarity that has enveloped France, Europe and elsewhere in the wake of the gun attacks in Paris in which 17 were killed may well be a defining moment in history. A nation and continent divided by politics, race, religion and economic standing have united in the name of a common cause, just as happened after the tragic events in the US on September 11, 2001. Millions of people, dozens of world leaders among them, took to the streets on Sunday, defiant that they would not succumb to fear and threats against freedoms. What happens next is as important, though: governments have to be careful not to further polarise those marginalised by poor policy-making. Calm has thankfully so far largely prevailed in the wake of the assault on the office of the satirical magazine Charlie Hebdo in which 12 died; and over the following two days, the killing of a policewoman and four people in a Jewish supermarket. All three gunmen, who died in shootouts with police, are believed to have had extremist Muslim links. The man behind the latter attacks left a video claiming he was avenging Western bombings of fighters of the group Islamic State in Iraq and Syria. There have since been a handful of anti-Muslim incidents in France and a German newspaper that reprinted the cartoons believed responsible for the initial shootings was firebombed. French President Francois Hollande has led calls for unity and protection of press freedom. The 40 presidents and prime ministers who linked arms on Sunday to show support sent the message that differences can be overcome. But rhetoric and symbolic gestures are meaningless without actions and in Europe and France in particular, joblessness and perceived discrimination has led Muslims to feel rejected by society. Some have turned to radical Islam. French intelligence and policing failed to prevent the killings; too late, they have been stepped up. Security officials from both sides of the Atlantic have vowed to coordinate surveillance and tighten border controls. US President Barack Obama will host a summit on February 18 to find ways to combat violent extremism. Anti-immigrant politicians have gone as far as to suggest a fresh war on terrorism, although that would be a mistake; it is that call, after the September 11 attacks, that led to the situation that the world now finds itself in. Extremist behaviour has to be kept in check, but immigrant and minority groups also have to be treated reasonably and fairly.