The explosions were the deadliest violence in the capital city of Colombo since 1996, the year that an explosion at Sri Lanka’s central bank killed almost 100. That attack was carried out by the Liberation Tigers of Tamil Eelam, otherwise known as the Tamil Tigers, a separatist group that for decades fought for an independent Tamil nation. It made suicide bombing a trademark of its fight.

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The Tamil Tigers fought for ethnic and national, not religious, reasons; in fact, some members of the group were Christian. Sunday’s attacks, which targeted churches on what is traditionally the holiest day of the year for Christians, seemed to be religiously motivated. And although the Tamil Tigers focused on the Sri Lankan state and society, some of Sunday’s blasts occurred at hotels, suggesting that foreign tourists were a target.

The tactic of turning a human into a weapon has been used at least since the days of the Russian empire. In 1881, Ignaty Grinevitsky, a member of the terrorist organization People’s Will, had planned with a colleague to throw a bomb at the czar Alexander II. The first bomb damaged a carriage, and the other man was arrested, but Grinevitsky was able to take another bomb closer to Alexander, killing the imperial leader — and himself.

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During World War II, in a far more organized fashion than People’s Will, imperial Japan used suicide bombers known as kamikaze pilots to intentionally crash their planes into Allied ships.

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But it was in the 1980s in Lebanon that suicide bombing as a phenomenon really began. In 1983, a suicide bomber drove a truck into a U.S. Marine base in Lebanon, killing 241 U.S. military personnel.

As it happened, several Tamil Tigers were training in Hezbollah terrorist camps in Lebanon at the time. Four years later, in July 1987, the Lebanon attack was essentially copied. A single driver, known as Captain Miller, drove a truck with explosives into a military base in Sri Lanka. The base had originally been a school near Nelliady, in Tamil territory, and the Tamil Tigers were determined to retake it from Sri Lankan forces. Between 20 and 40 people are thought to have been killed in the attack, which ultimately established Captain Miller as a Tamil hero.

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“The Tamil Tigers were the world’s leader in suicide terrorism from 1980 to 2003, carrying out more attacks than any Islamic group,” Robert Pape, a political science professor at the University of Chicago, told The Washington Post. In 2009, Pape said he counted 273 people he could verify killed themselves carrying out suicide attacks for the Tamil Tigers, about 130 more than Hamas had during “the life of their suicide campaigns.”

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The Tamil Tigers acknowledged carrying out 147 suicide attacks, according to a report by Action on Armed Violence, which conducts research and advocacy work to reduce global armed violence. (In 2000, Rohan Gunaratna, a security studies expert, estimated that 168 had occurred since 1983.) Attacks carried out by the Tamil Tigers killed former Indian prime minister Rajiv Gandhi in 1991 and Sri Lankan President Ranasinghe Premadasa in 1993.

The Tamil Tigers also pioneered the coordinated use of multiple suicide bombers at a single target. “They had a group of the Black Tigers that were especially proficient at these multiple coordinated attacks,” said Pape, author of “Dying to Win: The Strategic Logic of Suicide Terrorism.”

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The Black Tigers, Pape said, can be thought of as one might special forces, in that they achieved a level of prestige within the Tamil Tigers. The founder and leader of the Tigers, Velupillai Prabhakaran, famously had dinner with suicide bombers before they were sent off on their deadly missions. He celebrated the day of Captain Miller’s attack as Heroes Day.