By 1995 Abu Sayyaf was executing large scale bombings and attacks. In 1998 Abu Sayyaf founder Abdurajak Janjalani was killed in a gun battle, and his younger brother, Khadaffy Janjalani took over. Under his leadership, Abu Sayyaf increased their kidnappings, seeking to fund their operations through ransoms. They expanded operations into Malaysia in 2000.
In a summer 2014 video, senior Abu Sayyaf leader Isnilon Hapilon swore allegiance to Islamic State. However, analysts see Abu Sayyaf primarily as a local group with local interests and a very limited understanding of Islam. They are seen by their enemies and rivals as more of a gang of criminals than as true Islamists. The group is rejected by both Muslims and Christians because of its conduct, but clan-based kinship loyalties sustain it.
On January 27, 2019, Abu Sayyaf bombed a Roman Catholic Cathedral, killing 18 and injuring 82. After that, Philippine President Duterte declared an all-out war on Abu Sayyaf. After evacuating civilians, the Philippine army targeted them with massive airstrikes, artillery bombardments, and heavy ground operations.