Terrorist attacks have been increasing every year since the 1990s, and especially since September 11, 2001. All this goes back to the early 1970s, when OPEC (the Arab dominated oil cartel) was formed and the price of oil more than doubled. Most of the new cash went to Saudi Arabia and a lot of it was donated to Islamic charities. These groups, and the Saudi government, then sent money (to build mosques and religious schools) and missionaries to Moslem countries to spread the very conservative brand of Saudi Sunni Islam. This and the Iranian revolution of 1979 (that created a Shia Moslem religious dictatorship in Iran during the 1980s) are the cause of most of the subsequent increase in Islamic terrorism. The Islamic radicals were inspired, and able to network, in Pakistan during the 1980s, where the Saudis supplied billions of dollars for weapons and other supplies to support Afghan tribesmen fighting Russians in Afghanistan. Thousands of Islamic radicals from all over the world went to Pakistan to help out. Moslems pitched this as a jihad and a victory, despite the fact that the Russians left more because of economic collapse in the Soviet Union than anything else. But Islam has always thrived on fictional victories and that continues.
Despite the continuing popularity of Islamic terrorism, deaths from this malignancy peaked in 2007, and have been declining ever since. Thus the 7,473 terrorism deaths worldwide in 2011, were 25 percent less than 2007. What really set off the Islamic radicals in 2003, was the three week American campaign to remove Saddam Hussein from power. Although Saddam has always been a secular Arab despot (his Baath Party was founded after World War II in 1947) as a socialist revolutionary outfit. Baath was always hostile to Islamic radicals, but when Saddam invaded Kuwait in 1990, and the United States was called in (because the other Arab states in the region could not stop Saddam from coming after them), the Islamic radicals were enraged that infidel soldiers were allowed into Arabia by the local rulers. That anger simmered throughout the 1990s and skyrocketed when the U.S. went after Saddam (who had found religion after his 1991 defeat and had become host to all manner of Islamic terrorists). This led to a major terror campaign between Sunni and Shia radicals in Iraq, a battle which peaked in 2007, when the Sunni minority in Iraq admitted defeat and turned on the Sunni terrorists they had been supporting for the previous four years. Many of the surviving Sunni terrorists fled to Yemen, Somalia, and Pakistan. None of these places proved particularly hospitable and the short life of an Islamic terrorist is often spent in transit from one inhospitable sanctuary to another.
Islamic radicalism is a culture of death, for the true believers as well as Moslems they come across (and usually find insufficiently Islamic and thus worthy only of “involuntarily martyrdom”). About a third of the Islamic terrorism deaths in the last decade occurred in Iraq, which is still a battleground in the growing war between Shia (backed by Iran) and Sunni (backed by Saudi Arabia) Islam. This conflict goes largely unreported in the West but it is a major concern to most Moslems, even in countries where Moslems are a minority (and gangs of radical Shia and Sunni battle each other and is seen as just some more criminal gangs by the police).
Thus the effort by Iran to obtain nuclear weapons is not just a threat to the infidel (non-Moslem) West but more immediately to the oil-rich Arab states in the Persian Gulf. While these Arab nations are wealthier and better armed than Iran, the Iranians have more people and a long (several thousand years old) reputation for defeating Arabs militarily. The Arabs are intimidated by the Iranians. The Western allies of the Arabs may become less reliable as Persian Gulf oil is less needed (because of fracking) in the West. Thus the growing conflict between Shia and Sunni is becoming more of a factor in why and where Islamic terrorism shows up.