The Province of Lanao del Sur is the slightly bigger southern half of the former Province of Lanao.
During the American occupation of the Philippine Islands, the Philippine Commission implemented a national government and political reorganization. Pursuant to the provisions of Act No. 83 or otherwise known as The Provincial Government Act of 1901, Act No. 787 was approved on June 1, 1903 and made effective on July 15, 1903. Thus the Moro Province was created. The Municipality of Zamboanga was made as its capital (section 1).
On July 23, 1914, Act No. 2408 renamed Moro Province as the Department of Mindanao and Sulu. It took effect on September 1, 1914. The Municipality of Zamboanga was still the capital. The same Act also created the provinces of Agusan, Bukidnon, Cotabato, Davao, Lanao, Sulu, and Zamboanga (Section 19, Article 8, Chapter II).
On May 22, 1959, President Carlos P. Garcia approved Republic Act No. 2228 dividing the Province of Lanao into two: Lanao del Norte and Lanao del Sur. Marawi City was named as the capital of the Province of Lanao del Sur (Section 4).
On October 4, 1971, President Ferdinand E. Marcos approved Republic Act No. 6406 was which sought to create the Province of Maranaw out of the Province of Lanao del Sur.
The Province of Maranaw would have consisted the municipalities of Masiu, Poona-Bayabao, Lumba-Bayabao, Wao, Tamparan, Marantao, Kapai, Bubong, Ramain-Ditsaan, Mulondo, Saguiaran, Piagapo and Taraka.
Meanwhile, the Province of Lanao del Sur would have consisted the municipalities of Lumbatan, Butig, Bindayan, Bayang, Tubaran, Tugaya, Pagayawan, Pualas, Balabagan, Malabang, Ganassi, Madalum, Madamba, Bacolod Grande and Balindong.
The capital of the Province of Maranaw would have been Marawi City while the Province of Lanao del Sur would have been the Municipality of Malabang.
The division of the Province of Lanao del Sur was never implemented as the plebiscite that was called for its ratification was overrun by the imposition of Martial Law.
Note: This is part of LegendHarry‘s Oct 1-10, 2013 Zamboanga Peninsula-Northern Mindanao-ARMM-Davao Regions Backpacking Trip.