The evacuation of two major railway stations in Munich after an intelligence agency warned Germany of an imminent terrorist attack is not good news for Chancellor Angela Merkel who has used her New Year's speech to urge Germans to accept the influx of refugees not because it is a burden but because it is a duty. While the intelligence information - that suicide bombers from Daesh (the self-proclaimed IS) could target the central stations - might not be related to the refugees who poured into Germany in the summer, the incident will surely heat up the debate, especially among xenophobic groups. Merkel did not specifically mention Pegida, which has held large anti-Islamisation rallies in Germany, but the November attacks in Paris are still fresh in everyone's mind, particularly since at least two of the attackers entered Europe posing as refugees. Germany has taken in more than a million asylum seekers this year, almost half from Syria, far more than any other European country. The scale of the German undertaking is enormous. The government says that caring for the new arrivals will cost in the initial phase alone six billion euros. Then there is the problem of assimilation, from both sides. Thousands of refugees see this as a once-in-a-lifetime opportunity to come to Europe. Many of them fear the window will close. So many of the refugees will settle and stay, transforming the relationship between Europeans and people in the Middle East. The fact that many of the refugees are Muslims - not just Syrians and Iraqis but Pakistanis, Bangladeshis and Nigerians - is perceived as challenging Europe's identity. European societies could start to change rapidly as a result of immigration. The influx of migrants reinforces the German sense in particular that their identity is under threat. If ordinary Europeans become fearful that the nature of their societies will change, that fear will require enormous sensitivity on the part of Europe's and Germany's leaders to pass on their values to new arrivals who will inevitably want to pass on theirs. It is a historic challenge, and not necessarily a bad one. In August, Merkel said all Syrians could apply for asylum, and would not be sent back to the first safe country they landed in. Her handling of the refugee crisis has unnerved the German public and infuriated MPs, many of whom have demanded a cap on the number of refugees the country is prepared to take. Merkel has resolutely refused to budge. Her open-door refugee policy has cost her approval ratings and, as political criticism has mounted, it was openly asked whether the crisis might be her political undoing. The sheer numbers alone might prove impossible to manage. If so, then Merkel will be blamed for a profound miscalculation with implications for European unity. Germany and Germans have displayed an extraordinary amount of patience over the refugees. The government has demonstrated not just moral leadership, but the German people have shown great acts of kindness to the new outsiders. The vast crowds shuffling through the borders of Europe throughout the summer have been treated with disdain and in some cases brutality. In some other places like Germany, the warmth of the welcome they were accorded was in marked contrast to the hostility of others. Merkel herself has admitted that Germany was experiencing something that will change the country in the coming years. But there is growing criticism. The charge is that Germany has been dangerously naive and that its generosity has triggered a global migration that Europe will be unable to control. Still, despite the Munich station incident, as several leaders including Merkel have pointed out, Europe has a duty to offer asylum to those fleeing conflict.