RUTHFULLY YOURS

CANBERRA, Australia—Authorities said they disrupted a terrorist plot inspired by Islamic State to explode improvised bombs in central Melbourne on or around Christmas Day, with a railway station and a cathedral among the suspected targets.

Prime Minister Malcolm Turnbull said seven people were arrested, of whom five were expected to be charged over the plot. The plan allegedly involved the use of several improvised explosive devices, and a senior police chief said the accused plotters may have planned to use other weapons as well, including knives and a firearm.

Authorities alleged the suspects had scouted popular sites in Melbourne, Australia’s second-largest city and home to some 4 million people, as possible targets. The locations included the centrally located Flinders Street train station, St. Paul’s Cathedral and Federation Square, a popular riverside gathering place.

Mr. Turnbull called it “one of the most substantial terrorist plots” of recent years.

After a truck earlier this week plowed into a Berlin Christmas market, killing 12 people and injuring about 50 others, the Australian government ordered intensified security arrangements ahead of the Christmas and New Year celebrations, with state and national police on guard against a similar attack. Sydney holds large New Year fireworks celebrations each year, usually attracting more than a million people.

In the predawn hours of Friday, counterterrorism police raided several Melbourne buildings and arrested six men and one woman. Five of the men, all in their 20s, were expected to face charges including “acts in preparation of a terrorist event.”

Three appeared in a Melbourne court Friday, aged between 21 and 26, while two others were expected to face a judge on Saturday.

Australia’s five-tier terrorism threat alert system has been set at “probable,” the third-highest level, since September 2014. In December of that year, a lone gunman, later identified as Iranian immigrant Man Haron Monis, took over a central Sydney cafe and held numerous people hostage for 16 hours before police killed the gunman to end the siege. Two hostages—the cafe’s manager and a female customer—also died.

Since then there have been four attacks and 12 others disrupted. In September this year, police charged a 22-year-old man with committing a terrorist act and attempted murder after he allegedly stabbed another man multiple times in Sydney. In total, 57 people have been charged with terrorism-related offenses, Mr. Turnbull said. CONTINUE AT SITE

PARIS—The prime suspect in the Berlin truck attack arrived in Europe five years ago, at the leading edge of a wave of nearly uncontrolled immigration. That influx, culminating in the 2015 mass arrival of refugees, has exposed the region to security threats that will linger far into the future.

The path of the suspect—a 24-year-old Tunisian named Anis Amri who served jail time in Italy, then was detained briefly and released in Germany—has laid bare multiple failings in Europe’s security apparatus, including poor cooperation between national governments, porous borders and lack of biometric data to identify people who use false identities.

Compounding those problems, the rise of Islamic State and Germany’s decision to throw open the door to refugees last year has left security services overwhelmed as they try to track jihadist The attacks in Paris in 2015 and Brussels in March confirmed fears that Islamist groups had exploited refugee flows to smuggle operatives into the heart of Europe. Investigators have determined most of the assailants in those cases traveled from Syria through the Balkans and then Central Europe along with a river of refugees in the summer and fall of 2015.

Around the same time, Mr. Amri was released after four years in an Italian prison for starting a fire at a refugee shelter. The authorities ordered him to return to Tunisia. Instead, he headed to Germany, where he roamed freely using a series of false identities and sought asylum.

His path to Berlin is prompting calls for Europe to fix the longstanding security flaws of the Schengen Zone, which allows border-free travel throughout much of the region.

“We are very late, and we’re in the process of catching up,” said Georges Fenech, chairman of the French parliamentary committee that investigated the Paris attacks. “Because today, these terrorists move freely in the Schengen area. From the moment they enter with the migrants, they pass borders without much difficulty.”

Overtaxed security agencies dropped 24-hour surveillance of Mr. Amri this year when they failed to find enough evidence to make him a high-priority target. Mr. Amri had been under scrutiny after authorities discovered links between him and a radical cleric.

Police detained him in July when they discovered his request for asylum was denied and he was to be deported. But they released him a day later, because of Germany’s strict legal limits on the detention of migrants and Tunisia’s unwillingness at the time to take him back. CONTINUE AT SITE

German investigators have named a Tunisian refugee, Anis Amri, as the jihadist whom they suspect carried out Tuesday’s mass-murder attack. Amri is believed to be the man who drove a truck through a Christmas festival in Berlin, killing twelve and wounding four-dozen others in an atrocity reminiscent of the attack in July, when 86 people were killed at a Bastille Day celebration in Nice.

Notwithstanding that they arrested and held the wrong man for several hours, it turns out that German authorities have been well aware that Amri posed a danger. He is yet another of what my friend, the terrorism analyst Patrick Poole, has dubbed “known wolves” — Islamic terrorists who were already spotlighted by counterterrorism investigators as likely to strike.

Amri, who is variously reported to be 23 or 24, arrived in Germany in July 2015 as an asylum-seeker. He was able to remain because of Chancellor Angela Merkel’s suicidal open-door policy for refugees from the Muslim Middle East and North Africa. Prosecutors in Berlin attempted to deport Amri back in June, after learning three months earlier that he was planning “a serious act of violent subversion.” He is reportedly a follower of Abu Walaa, an Iraqi sharia-supremacist firebrand who was recently arrested on suspicion of being a top ISIS leader and recruiter in Germany.

His terrorist activities aside, Amri has also been involved in narcotics trafficking, theft, and the torching of a school. That last felony occurred in Italy, where the “refugee” was sentenced to five years in prison before being welcomed into Deutschland. All that baggage, and still the Germans allowed him to remain. Reportedly, officials felt they could not deport him because he did not have a passport and the Tunisian government would not acknowledge him (despite the fact that the Tunisian government had convicted him in absentia of a violent robbery). That might explain a brief delay in repatriating him; it does not explain a legal system that permits a suspect with a lengthy, violent criminal record to remain at liberty while he is suspected of plotting mass-murder attacks.

Yesterday’s atrocity highlights an aspect of the refugee crisis to which I have been trying to draw attention for over a year: The main threat posed by the West’s mass-acceptance of immigrant populations from sharia cultures is not that some percentage of the migrants will be trained terrorists. It is that a much larger percentage of these populations is stubbornly resistant to assimilation. They are thus fortifying sharia enclaves throughout Europe. That is what fuels the jihad. It would be foolish to think it couldn’t happen here, too.

To be sure, the infiltration of trained terrorists is a huge problem; even a small percentage would compute to thousands of jihadists within the swarms of migrants. Alas, that is a secondary concern. The bigger threat is the enclaves.

These are not merely parallel societies in which the law and mores of the host countries are supplanted by Islamic law and Islamist mores. Even residents who are not jihadists tend to be jihadist sympathizers — or, at least, to be intimidated into keeping any objections to themselves. That turns these neighborhoods into safe havens for jihadist recruitment, training, fund-raising, and harboring. They enable the jihadists to plan attacks against the host country and then elude the authorities after the attacks.