Approximately one million Muslims have flooded into Europe in the past year, the majority having been admitted by Germany in a grand humanitarian gesture. Haunted by visions of its Nazi past and its central role in the Holocaust, Germany’s chancellor, Angela Merkel, has urged Europeans to emulate her example.

Merkel’s openness to the migrants, many of whom are Syrians fleeing an increasingly destructive civil war, is commendable on one level. But has she committed a grave error of judgment that Germany will deeply regret in the years ahead?

The refugees, particularly the Syrian ones, hail from countries steeped in totalitarianism and antisemitism. The social and political attitudes they bring with them may well clash with the liberal values that many Europeans cherish. This situation will surely spell trouble in the not-too-distant future.

This week’s suicide attacks in Brussels, which claimed the lives of 31 people, should give us pause because they were planned and orchestrated by Belgium citizens of Muslim descent, among them being Khalid and Ibrahim el-Bakraoui. By all accounts, the killers were acting on behalf of Islamic State, which reportedly has a considerable following in Belgium’s Muslim community.

Belgium has become an incubator of native-born Muslim radicals, and this phenomenon should be a source of immense concern to the authorities. Lest it be forgotten, the attacker who stormed into the Jewish Museum in Brussels a few years, killing four visitors, was a Muslim extremist holding Belgian nationality.

Belgium, however, is hardly unique.

Last November’s terrorist rampage in Paris, which resulted in the deaths of 130 Parisians and foreigners, was carried out by a team of Islamic State-affiliated European jihadists, as was the deadly Charlie Hebdo assault by the Kouachi brothers. The 2012 attack on a Jewish school in Toulouse was perpetrated by a European jihadist, too.

Thousands of European Muslims have gone to Syria to join the ranks of Islamic State, the Al-Nusra Front and other extremist organizations fighting to unseat the regime of President Bashar al-Assad and replace it with a polity based on Sharia law. The fighters who return to Europe from the Syrian battlefields have been thoroughly brainwashed and pose a clear and present danger to European societies.

It’s an issue that European leaders will have to deal with in a systematic, even ruthless, manner. It may be politically incorrect to say, but Europe cannot afford a Fifth Column of subversives and traitors in its midst.

Muslim leaders in Europe bear an inescapable responsibility for monitoring and combating the jihadist movement within their insular communities. They cannot close their eyes and ears to radicalized Muslim men hell-bent on wreaking havoc in the name of Islamic fundamentalism, which has morphed into one of the greatest threats facing Western nations today.

This threat, in particular, affects the safety of European Jews, judging by two recent reports.

The American Jewish Joint Distribution Committee has released a report stating that 40 percent of European Jewish community leaders fear that antisemitism is the most serious problem facing Jews in contemporary Europe.

Muslims, ominously enough, have been in the forefront of attacks against Jews and Jewish institutions in the past few decades. White European fascists are hostile to Jews, as they have been for centuries, but of late they have refrained from physically attacking them. Muslim thugs have appropriated this unsavoury role.

The Ministry of Education in Holland has acknowledged that antisemitism has infected a number of Muslim students in some Dutch schools. “Antisemitic behavior is a recurrent problem in some schools,” wrote Margalith Kleijwegt, the author of a study commissioned by the government. “The (Muslim) pupils receive anti-Jewish attitudes at home.”

Dutch Education Minister Jet Bussemaker has said that this “painful” manifestation of racial hatred must be confronted and dealt with “in accordance with democratic values.”

The sooner, the better.

Most Muslims in Europe are peaceful, law-abiding citizens who just want to get on with their lives, but a small and dangerous core of homegrown jihadists are roiling the waters and causing problems for their co-religionists. They should be exposed, rooted out and dealt with expeditiously.

Failure to do so will lead to more French and Belgium-style atrocities in the streets of Europe.