warning that "our jihadists have arrived in Nigeria from Somalia where they received real training on warfare from our brethren who made that country ungovernable", which analysts understood as an allusion to cooperation with al-Shabaab. However, in the view of some observers, most consequential are al-Shabaab's links to al-Qaeda in the Arabian Peninsula (AQAP). AQAP is based in Yemen, which has longstanding ties to Somalia, and analyst Katherine Zimmerman told the U.S. Congress that AQAP "almost certainly provided the equipment or the expertise" for al-Shabaab's 2016 laptop bomb. Islamic State In early 2015, the Islamic State of Iraq and the Levant (ISIL) published online the first of a series of videos aimed at al-Shabaab, calling on the group to switch allegiances from al-Qaeda to ISIL and its leader Abu Bakr al-Baghdadi. These public appeals had reportedly been preceded by informal ISIL attempts to establish a relationship with al-Shabaab. Yet al-Shabaab publicly ignored the overtures. By September 2015, it had issued an internal memo, directed at pro-ISIL elements in its ranks, reaffirming the group's allegiance to al-Qaeda and banning any discussion about ISIL. The group also detained several fighters who had voiced support for ISIL. In October 2015, senior al-Shabaab commander Abdul Qadir Mumin and approximately 20 of his followers in Puntland pledged allegiance to ISIL, establishing what became Islamic State in Somalia (ISIS). Further defections in al-Shabaab ranks occurred in the border region between Somalia and northern Kenya, leading the head of al-Shabaab in the Lower Shabelle region, Abu Abdalla, to announce that all pro-ISIL members should leave the group or be killed. The groups clashed violently on several occasions, most fiercely during 2015, and al-Shabaab's internal security service continued to arrest, and sometimes execute, suspected ISIS supporters within al-Shabaab's ranks. Violent conflict between the groups was reinvigorated in 2018 by ISIS provocation, and, in December, al-Shabaab's spokesman announced an offensive – code-named Operation Disease Eradication – against ISIS. The same week, al-Shabaab's general command, released an 18-page treatise rebuking ISIS's ideology and listing crimes it had committed under the Quran. Sources of income and arms In 2020, the Hiraal Institute estimated that al-Shabaab collected at least $15 million in revenue every month, implying revenue on a similar scale to the government's; and the UN estimates that the group's military budget was approximately $21 million in 2019. In the period after 2014, al-Shabaab established its own Ministry of Finance, and