Europe has changed greatly in the past two weeks. Two weekends ago, as in any major American city, European capitals were buzzing with positive energy. Today, the positivity has been purged by fear. Friday, November 13: A night that saw 130 civilians murdered in Paris. Monday, November 16: A day that saw hundreds of police raids across Europe, and a bloody shoot-out in a Paris suburb. Saturday, November 21, and Sunday, November 22: Facing a Paris-style atrocity, Brussels goes into lockdown and public spaces are relabeled death traps to be avoided.

Europe has changed. And as a new week begins, Brussels’s colleges, schools, and metro are shuttered. Even absent a direct attack, the civic heart of a historic democracy has been damaged. Belgian authorities clearly believe that a cell (or cells) of heavily armed terrorists — very likely connected with the same plotters responsible for the Paris attacks — are preparing to strike. In other major EU capitals, including Berlin and London, authorities are working on overdrive, hunting other ISIS cells that might be ready to launch an assault. Yet Europe’s terror is not peripheral to America; it requires more than our sympathy. Now empty of life, the coffins of Paris and the streets of Brussels prove ISIS’s existential threat to our way of life. Last night, I spoke with a close friend who lives in Brussels. I asked her how people are feeling.

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“Unsure and unsafe,’’ she told me. “The atmosphere is very heavy. People are anxious about their safety, and wondering if Belgium is a secure place to raise children. We are quite angry, as there have been many warning signs that terrorism should be fought here, on the ground. I guess what we really need now is to feel that the government is doing what it should.”

My friend’s words reflect the immense psychological stress Europeans are under, and they highlight how the bond between public and government has been severed by fear. We must contemplate the consequences. First, we must recognize that through one brutal atrocity and the credible threat of looming attacks, ISIS has successfully frayed the Democratic contract that underpins Western civil society. This fraying of the civic fabric should remind us that confronting ISIS’s ideology requires vigorous free speech rather than political correctness. Second, this social breakdown also reminds us that ISIS is not a criminal organization, but rather a political entity that has earned support even in the very European cities it is now attacking. (When the Brussels plotters are caught, we’ll probably learn that they were given safe haven by some in their local community.)

Events in Brussels and Europe call for more than contemplation. They call for our action. After all, while Europe’s security is an American concern for reasons of history and shared values, ISIS’s threats in Europe directly endanger the hundreds of thousands of Americans who live there.

Facing the security crisis in Europe, America has a clear imperative: We must lead a coalition to efficiently annihilate ISIS. It has to be us. Only America can drain ISIS of its sectarian power and support a Sunni uprising. The alternative is President Obama’s containment strategy, and that may lead to more coffins like those in Paris, the self-seclusion of millions, and a strengthening of the ISIS empire.

— Tom Rogan is a writer for National Review Online and Opportunity Lives, a panelist on The McLaughlin Group, and a senior fellow at the Steamboat Institute. He tweets at TomRtweets. His homepage is tomroganthinks.com.