The question as posed is difficult to answer, because "largest" can mean a lot of different things as can "terrorist".
If the word "largest" is meant to mean most ubiquitous, then the answer is certainly Al Qaeda, especially since the American Invasion of Iraq. Al Qaeda operates like a McDonald's, Franchising cells across any country in which it exists. In addition, smaller jihadist organizations will reach out to Al Qaeda for funding and the name recognition. In return, Al Qaeda will claim that this smaller independent jihadist organization is part of its ranks, even though their objectives may be different than those of the Al Qaeda leadership.
If the word "largest" is meant to mean the largest internal membership, then the answer is a lot murkier. Accurate accounts of organizational membership almost never exist because the cell structure is loose. In addition, most individuals so affiliated only know the names of those fellow group members that they are very close to so as to limit the efficacy of post-capture interrogation. This makes it different to properly estimate a single cell, let alone figure out how extensive the cell network is.
How did ISIS become such a wealthy terrorist group
choose 3 from this group? Are there any terrorist groups in the area? Will the local population warn Americans? How many members are there in a known terrorist group? Is the reported terrorist group predictable?
Billie the Kidd's organization. KKK
Butty group
Simply it is a terrorist group.
Today, unfortunately not; but the activities of the Hungarian irredentists can be characterized as terrorist.
There is no terrorist group with its base of operations in Israel, but numerous Palestinian terrorist groups aim their violence towards Israel and intend to kill Israelis. The last Zionist Terrorist Group was the Irgun, which was disbanded in 1949.
FARC
terrorist group in Iraq
NDFB
from a group of terrorist
FARC