Islamic jihad is on the rise, due to the US becoming too weak after the trillions spent in Iraq and Afghanistan to fight it.
That's why you have Boko Haram in Nigeria kidnapping Christian girls for forced marriages, Al Shabab in east Africa, Muslim mobs killing atheists in Pakistan and Bangladesh, ISIS in Syria, resurgent Muslim separatists in Indonesia and the Philippines, Muslim Urgyurs blowing up buses in China.
This is not generic "terrorism", it is many different Muslim groups around the world seeking to spread Islam and Islamic rule around the world by the sword (or suicide bomber), as the faith spread through most of its history. Indonesia converting by missionaries was the exception to Islam's violent conquest from the Mecca period to today.
One reason Islamic terrorism can spread so far is the spread of Muslim "refugees", students and immigrants - and second generation Muslims who have settled around the world are more likely to support implementing Shariah law and spreading Islam by the sword than their somewhat secularized parents.
Calling it "transnational terrorism" is like saying it is "extremism".. Extreme Buddhists are utterly peaceful, as are fundamentalist Christians like the Amish. Only in Islam is becoming fundamentalist equated to killing people, even if it is only immediate like the 90% of honor killings committed by Muslims.