Which earthquake caused the greatest number of fatalities from a tsunami in one event?

The Indian Ocean tsunami generated by the 2004 Sumatra earthquake killed hundreds of thousands of people across many countries. The waves struck with little warning because the region lacked a mature tsunami alert system at the time. Coastal communities in Indonesia were hit especially hard, and the disaster led to major international relief and reconstruction efforts. It became a turning point in global tsunami preparedness, prompting new warning systems and education programs. The event showed how subduction-zone earthquakes can create far-reaching humanitarian crises.