History.com: How the Troubles Began in Northern Ireland

For 30 years, Northern Ireland was scarred by a period of deadly sectarian violence known as "the Troubles." This explosive era was fraught with car bombings, riots and revenge killings that ran from the late 1960s through the late 1990s. The Troubles were seeded by centuries of conflict between predominantly Catholic Ireland and predominantly Protestant England. Tensions flared into violence in the late 1960s, leaving some 3,600 people dead and more than 30,000 injured. While Ireland was fully independent, Northern Ireland remained under British rule.