Isabela, Basilan in the context of "2019 Bangsamoro autonomy plebiscite"

Zamboanga Peninsula (Cebuano: Lawis sa Zamboanga; Chavacano/Spanish: Peninsula de Zamboanga; Filipino: Tangway ng Zamboanga), designated as Region IX, is an administrative region in Mindanao, Philippines. It consists of the provinces of Sulu, Zamboanga del Norte, Zamboanga Sibugay and Zamboanga del Sur, and the cities of Isabela and Zamboanga City.

The region was previously known as Western Mindanao. Pagadian serves as the regional center, while Zamboanga City is the region's commercial and industrial center.

The Autonomous Region in Muslim Mindanao (Filipino: Rehiyong Awtonomo ng Muslim Mindanao; Arabic: الحكم الذاتي الاقليمي لمسلمي مندناو Al-ḥukm adh-dhātī al-'iqlīmī li-muslimī Mindanāu; ARMM) was an autonomous region of the Philippines, located in the Mindanao island group of the Philippines, that consisted of five predominantly Muslim provinces: Basilan (except Isabela City), Lanao del Sur, Maguindanao, Sulu, and Tawi-Tawi. It was the only region that had its own government. The region's de facto seat of government was Cotabato City, although this self-governing city was outside its jurisdiction.

The ARMM included the province of Shariff Kabunsuan from its creation in 2006 until July 16, 2008, when Shariff Kabunsuan ceased to exist as a province after the Supreme Court of the Philippines declared the "Muslim Mindanao Autonomy Act 201", which created it, unconstitutional in Sema v. COMELEC and Dilangalen.

Basilan, officially the Province of Basilan (Chavacano: Provincia de Basilan; Yakan: Wilayah Basilanin; Tausug: Wilaya' sin Basilan; Filipino: Lalawigan ng Basilan), is an island province of the Philippines located primarily in the Bangsamoro Autonomous Region. Basilan Island is the largest and northernmost of the major islands of the Sulu Archipelago. It is just off the southern coast of the geographic Zamboanga Peninsula.

Isabela, the most populous city and the former capital, is a component city under the provincial government of Basilan but is administered as part of the Zamboanga Peninsula Region and is listed statistically independent. The provincial capital has since been transferred to Lamitan. Despite this, some national government offices are still located at Isabela.