Time gaps existed in the first three waves between precipitating political events and the development of terrorist activity. But now the time gap has disappeared because the precipitating events were directly associated with terrorism. All of those events occurred in the Islamic world where religion was employed to justify terror. Jewish, Sikh, and Christian terror groups emerged very quickly afterwards, but Islamic groups were larger, more durable, and had a more significant global impact. The international world changed; Iran’s religious revolution made it a major player; and the Soviet Union’s collapse intensified Islamic opposition to the United States. Sikh, Jewish, and Christian terrorists came from a national base, but Islamic ones often emerged from many countries to join a particular group; and two critical groups, al-Qaeda and ISIS, aimed to re-establish a caliphate embracing the Islamic world. Diasporas provided financial support as they had in other waves, but some Islamic immigrants, like first wave anarchists, employed terror in their new homes and often left those homes to seek targets elsewhere. “Suicide bombing” or “self-martyrdom,” the wave’s distinguishing tactic, made it the most destructive wave. The only religious groups to embrace this tactic were Islamic, though ironically, the secular Tamil Tigers used it and did so more often than any Islamic group did. Islamic groups initiated social services for their societies, a program not seen earlier, and the Tamil Tigers adopted social services for their communities as well. Al-Qaeda, born in the resistance to the Soviet Afghan invasion, became the wave’s most important group. After difficulties in helping uprisings outside Afghanistan in the Islamic world, it decided to strike the United States, and its 9/11 attacks, the wave’s high point, are the most destructive terrorist acts ever. The United States then invaded Afghanistan forcing al-Qaeda to leave that country. Instead of completing the job, however, the United States decided to invade Iraq to prevent Iraq from giving al-Qaeda weapons of mass destruction, weapons Iraq did not have. This over-reaction inflamed Muslims everywhere, enabling al-Qaeda to get more recruits and develop Iraqi resistance. One crucial focus of al-Qaeda in Iraq was its gruesome atrocities towards the Shia population, which produced violence between Sunni and Shia throughout the Islamic world. The United States ultimately eliminated al-Qaeda in Iraq, and al-Qaeda Central was unable to get another ground base. Al-Qaeda Central then adopted two methods to revitalize itself. The lone wolf strategy, developed first by U.S. Christian terrorists, did not produce many significant results. At the same time, many franchises were created but each focused on local activities and did not strengthen al-Qaeda’s global capacities. A new situation developed with the “Arab Spring” in 2011, when peaceful secular demonstrations for equality and democracy were transformed into violent conflicts between Shia and Sunni sects. Syria, the bloodiest scene, attracted support from Shia and Sunni elements everywhere and encouraged Russia and the United States to get engaged. ISIS (Islamic State), the remnant of al-Qaeda in Iraq, was reborn and grew immensely there as it captured much territory in Iraq and Syria and became the wave’s most important group. Al-Qaeda Central also became involved and eventually turned against ISIS. In a short time ISIS lost most of the territory gained, and its European strikes to get the West more deeply involved in the conflict by sending troops to Syria and Iraq failed. Al-Qaeda and ISIS franchises continue to fight each other, a conflict that may end the wave.