The European Union needs to reinvent its security system. It needs to break the stovepipes that prevent sharing information, enforcing borders and protecting citizens. In the months before Tuesday’s terrorist attacks in Brussels, “the system was blinking red,” as George Tenet, the former CIA director, famously described the period before Sept. 11, 2001. Yet Belgium (like pre-9/11 America) couldn’t connect the dots.

The jihadist wave rolling back toward Europe is dizzying: U.S. intelligence agencies estimate that more than 38,000 foreign fighters have traveled to Iraq and Syria since 2012. At least 5,000 of them came from Europe, including 1,700 from France, 760 from Britain, 760 from Germany and 470 from Belgium, according to official data collected by the Soufan Group, a security consulting firm. Relative to its population, Belgium spawned the largest number of these fighters.

Belgian authorities couldn’t find Salah Abdeslam , the logistical planner of the November Paris attacks, for more than 120 days — until they finally nabbed him Friday a few blocks from where he grew up in the Arab enclave of Molenbeek. He was hiding in plain sight. But Belgium’s failure was cooked into the system: The jihadists move stealthily, and the Belgians didn’t collect or share enough of the intelligence that was there. Authorities had allowed Molenbeek to become a haven — more dangerous to Belgium than even the jihadists’ sanctuaries in Syria, Iraq and Libya.