From New York Magazine’s Intelligencer:
ISIS is now well known for its widespread appeal to individual jihadis around the world. As the New York Times noted on Friday, “the black standard of the Islamic State has been popping up all over” in Pakistan lately. But beyond the lower-stakes demonstrations of popular sympathy, about a dozen militant organizations in nine countries (in addition to Iraq and Syria) have made formal pledges of support to the group, making them, in a very real sense, part of ISIS’s fighting force. Think of them as ISIS’s self-appointed foreign bases.
Veryan Khan, the editorial director of the Terrorism Research & Analysis Consortium, explained the process to Intelligencer. Support for ISIS among other radical groups, she said, manifests in one or more of three ways. At the most basic level, members of a group can show support for ISIS ideology by sporting the group’s flags and logo. Groups that are more committed can pledge loyalty to ISIS, which Khan describes as a symbolic statement that doesn’t really confer any type of formal alliance. The most committed make a formal declaration of bay’ah, or allegiance, and become official allies. (Such pledges were historically given to caliphs.) What shape, exactly, these alliances take can vary, in part based on the distance between Baghdadi and central leadership in the group. However, groups “don’t have to fall into the top category to be strong supporters,” Khan cautioned.
TRAC has identified at least 12 groups outside Iraq and Syria that have made a formal pledge of allegiance to ISIS and Baghdadi. (There may be more who have done so without publicizing such an agreement.) While some of them are large, established groups, others are comparatively new and unknown. In most cases, precise membership numbers are not available.
See the country-by-country list here.