In September 1972, Marcos proclaimed Martial Law in the Philippines, declaring that it was necessary in order to meet the threat to national security posed by the Communist Party, the New People’s Army, and the secessionist struggle of certain Moslem elements in Mindanao and Sulu.
Since then he has governed by a system of authoritarian personal rule, supported by the armed forces, and reinforced by a new constitution which he has introduced without the approval of Congress. These actions have been approved in a series of referenda, the validity of which has been seriously challenged.
Philippines-martial law-fact-finding mission report-1977-eng (full text in English, PDF)