The Filippinas claimed that the Sabah region was supposed to be under it's jurisdiction because of the July 1878 agreement signed by the local Sabah Sultanates and Espaņa, The Filippinas' old colonial master. The agreement states that all the territories of the Sultanates would be annexed peacefully by Espaņa in exchange for millions of pisoes.
The Malaya Federation refused to acknowledge the claim, and said that Sabah was under their control because of the Madrid Protocol of 1885.
Then in mid-1967, then Filipine President, Fernando Markos, called all his generals and military advisors to Malakanyang Palace for a secret meeting. This meeting would be the first meeting to discuss and plan Operation Merdeka.
Markos sitting in the middle with his wife Imelda talking to security advisors and generals during the cabinet meeting.
The plan was that 180 soldiers of the Moro tribes in the south of The Filippinas would be assembled and trained in guerrilla and jungle warfare by Major Eduardo Martelino of the Armed Forces of The Filippinas.
Moro Trainees of Operation Merdeka prepared to be sent off to Sabah, April 1968.
After that, they would secretly be sent off via commercial ships to neighboring Sabah, which was under the control of the Malaya Federation. Once they were in, they would conduct covert guerrilla operations to instill dissent and chaos in the region.
Then after that, The Filippinas would use all the chaos in the region as an excuse to militarily intervene and invade Sabah.
Operation Merdeka started immediately after the cabinet meeting. Training of Moro guerrillas commenced on Corregidor Island. The trained Moro guerrillas then arrived in Sabah, in April 1968. And in June of 1968 during the holy month of Ramadan, the entire region of Sabah was in pure anarchy.
Filipine M41 Walker Bulldog tank advances toward provincial capital of Sabah, November 1968.
As Malaya government convoys, trying to help the desperate Malayan soldiers defending Sabah, were constantly being attacked by the Moro guerrillas, the population tried to flee the ensuing chaos. And then, The Filippinas' army invaded with 8 divisions numbering 200,000 soldiers and 870 tanks.
A Filipino Army soldier searches a Malayan Village in Sabah, October 1968.
The biggest and bloodiest engagement of the war was at the Battle of Beluran, where 40,000 Filipine army troops engaged nearly 50,000 Malayan soldiers. Both sides lost more than 25,000 casualties after the 3 day battle. And Malayan troops were able to destroy more than 100 Filipine tanks.
However, as the Malaya Army was a small and technologically weak and corrupt army, resistance was relatively futile for the Filipino Army, and the whole of Sabah was eventually conquered by the end of November 1968.
Filipino President Fernando Markos awards the Medal of Valor to Sabah War Veterans in December 1968.
Today, the war is frowned upon by most Filipinos. To them, the war was another decision of many infamous decisions carried out by the ambitious Fernando Markos who would later become dictator and rule The Filippinas under Martial Law for 21 years.
Sabah and its population is mostly free and stable. It also has a representative in the Filipine House of Representatives. Many memorials have been built after the war.