Bataclan Theatre Attack (Paris, 2015)

The Bataclan Theatre Attack killed 90 concertgoers in a coordinated assault that exposed European venues' vulnerability to armed threats—a failure 3 times deadlier than the Manchester Arena bombing (#1). Attackers entered with Kalashnikovs and suicide vests, bypassing a single unarmed security guard, and the attack lasted 20 minutes before police intervention. Post-incident analysis revealed that 78% of Parisian venues had no armed security protocols, and security upgrades cost €40 million nationwide. The attack's death toll remains the highest for a single concert event in Europe.