PARIS • When I moved to Europe 12 years ago, my biggest concern was whether I would ever speak decent French. Practically every American I knew came to visit, many saying they dreamt of living here too.

I did not worry much about far-right political parties or the European Union (EU). I certainly did not fret about terrorism. That now seems like a long time ago.

One of the most upsetting facts about the bombings in Brussels on Tuesday was how unsurprising they were. One day earlier, Belgian Interior Minister Jan Jambon had gone on national radio and warned that his country faced a "credible and imminent" threat of attack.

The next morning, Islamic State in Iraq and Syria (ISIS) operatives detonated bombs in a departure hall at Brussels Airport and on one of the city's main metro lines.

The bombs killed at least 31 people and injured about 300 more.

A 47-year-old woman told the French newspaper Liberation that, after seeing the explosion on the metro, she closed her eyes and told herself: "This is it. I am in the attack that we've been talking about for months."

A Belgian friend said that at dinner that night, her 14-year-old daughter explained: "At school, we knew that Brussels would be the next target. The terrorists just waited for us to let down our guard."

The most emblematic photograph of the aftermath showed survivors walking in a dark tunnel along the tracks of the metro.

The image incarnates the current European nightmare: You are buying groceries, commuting to work or checking in for a flight, and then suddenly you are not.

It is hard to adjust to this new reality. An emergency room doctor told me that before last November's attacks on Paris - in which teams of men exploded suicide belts and fired Kalashnikovs on people in cafes and at a concert - many of his colleagues had rarely, if ever, seen a gunshot wound. The few they had encountered were usually suicides from hunting rifles.

To Europeans, Brussels was supposed to be a dull place that you did not have to think much about until you had to change planes there.

There is a parlour game in which you stump people by asking them to name 10 famous Belgians.

"Brussels, the anti-fanatic attacked by the fanatics," French journalist Laurent Joffrin wrote in Wednesday's Liberation.

"Brussels, a cousin whom one is content to know is there."

Right after an attack, it is easy to say that everything feels different. People are horrified. Parents keep their kids home from school.

Newspapers run headlines like "Europe at war". There is the sad, familiar search for a slogan.

This time, I prefer the Belgian frites arranged to make a rude gesture resembling a finger, and the banner reading, "Je suis sick of this", followed by an expletive.

But soon, for most of us, life returns to normal. A spate of juice bars just opened in my Paris neighbourhood. The department store Le Bon Marche is staging an exhibition on the kooky American fashion icon Iris Apfel. Europe still has lots of pretty capitals with rivers running through them.

The French seemed especially determined that nothing should change too much. Late last year, alarmed by news reports saying that schools could be targets of future attacks, I e-mailed the parents' committee at my children's school.

I suggested that, in the light of the threat, we meet to discuss how to improve security.

When almost no one replied, I wondered if I was having an American overreaction. One father lectured me on the sidewalk about how schools ought to be open places. The school's director initially told me that he did not think any changes were necessary. A few months later, a group of parents did organise to deal with a separate crisis: Their second-graders had not learnt to conjugate the verb "etre".

But Europe does feel like a different place than it did a year ago. And it is not just the threat of bombs in suitcases. It is also the related crises that are hitting the continent all at once. More than a million migrants and refugees have arrived here in the past 15 months, mostly from Syria, Afghanistan and Iraq.

Never mind that these refugees are fleeing far worse violence than what we are now seeing in Europe, and that it is often carried out by ISIS too.

Europe's far-right parties are getting stronger by demonising them.

All this is testing whether the EU - which most people here could once safely ignore - will hold together. Britons will vote in June on whether to stay in the union.

In a recent survey, a majority of French people said they would like to hold a referendum here too.

And while governments are claiming worrying new powers to stop terrorism, they have not agreed on how to share intelligence, they are not sure how members of Franco-Belgian terrorist cells communicate with one another, and they do not even agree on how to transliterate foreign names to track people across borders.

Salah Abdeslam, who helped orchestrate the attacks on Paris, managed to slip out of the country afterwards. Four months later, he was found hiding in Molenbeek, the Brussels neighbourhood where he grew up. That is one of the hardest facts to reconcile: These are Europeans attacking their own homelands.

Roughly 5,000 EU citizens have fought in Syria, and most come from four countries - France, Germany, Britain and Belgium.

Their lives sound very familiar: Abdeslam was apparently caught after the police noticed a suspiciously large order for a pizza delivery.

The three men who planned to bomb Brussels Airport were briefly stymied when a Brussels taxi company sent the wrong type of car to take them there.

Even their motivations are recognisable. According to ProPublica, a Belgian militant who was training in Syria called his mother to ask what people in Molenbeek were saying about a 20-year-old friend who blew himself up outside the Stade de France.

"Are they talking about him?" he asked. "Are they praising him? Are they saying he was a lion?"

Europeans are becoming more vigilant. A friend in Berlin said that on a recent train to Dusseldorf, the passengers and crew got nervous when no one claimed a suitcase left by one of the doors. A bomb squad met the train at its next stop and told passengers they would be herded into a secure area. Just then, the old Turkish man who owned the suitcase woke up and revealed its contents - a pile of clothes.

Despite the inevitable false positives, it is hard not to be on guard.

I am constantly making a series of mundane existential calculations: Is it worth it to risk going to a movie? Should I let my kids ride the metro to soccer practice?

Daily life has a chiaroscuro quality: One minute, you are riding a bus and enjoying a view of the river. The next minute, you are wondering about the fellow with an unusually large backpack.

This has made it a terrible time to be a dark-skinned European man in his 20s. Discrimination was a problem before terrorism. Now, the bad deeds of a few people have made life worse for millions.

I heard about an exasperated passenger in Paris who got so many suspicious looks in the metro, he slowly emptied the contents of his bag to reassure the other riders that he was not carrying a bomb.

As the European fantasy has dimmed, I hardly get any foreign visitors anymore. A relative who came from New York recently told me that her trip to Paris was an act of solidarity. My mother wants me to leave France altogether.

The French are learning to live with more security. Guards now search bags - or at least glance into them - at the entrances to theatres and department stores.

High school students are allowed to take their cigarette breaks on school grounds, as it is too risky to let them gather outside the school gates. There has been a big fuss about a government proposal that seems unlikely to deter attacks: being able to strip convicted terrorists of their French nationality.

Since the bombings in Brussels, Europeans are demanding more practical measures. Israeli security experts are being consulted.

There is talk of more intelligence-sharing between governments. The headline on the cover of Thursday's Le Parisien was "What must be changed now".

But the truth is that, for everyone here, a lot has changed already.

NEW YORK TIMES

•Pamela Druckerman is the author of Bringing Up Bebe: One American Mother Discovers The Wisdom of French Parenting, and a contributing opinion writer to NYT.