The 1970 Bhola cyclone devastated much of the region, killing an estimated 500,000 people. More than half the city of Dhaka was flooded and millions of people marooned. With public anger growing against ethnic discrimination and poor cyclone relief efforts from the central government, Bengali politician Sheikh Mujibur Rahman held a nationalist rally on 7 March 1971 at the Race Course Ground. An estimated one million people attended the gathering, leading to Ziaur Rahman's 26 March declaration of Bangladesh's independence. In response, the Pakistan Army launched Operation Searchlight, which led to the arrests, torture and killing of hundreds of thousands of people, mainly Hindus and Bengali intellectuals.