[5][6][7] Simbulan's influence and reputation led to his being held by the Marcos regime as a political prisoner at Fort Bonifacio and Camp Crame for more than two years without charges.

[3][6] Simbulan was increasingly disillusioned by what he experienced in the field, including financial practices which were unfair to the rank and file, lack of respect for AFP personnel by American forces stationed in the Philippines at the time, and the fact that people ran away in fear whenever soldiers arrived in their villages.

[3] During this time he became a strong influence on a number of cadets who later played significant roles in Philippine history, including Victor Corpus and Crispin Tagamolila, who would defect to the New People's Army; and Rodolfo Biazon, who would become Armed Forces of the Philippines Chief of Staff and later a two-term Senator.

Despite already being a full colonel, Simbulan resigned his commission and his teaching post in the years leading up to martial law.

[9][7][6] Simbulan authored several books on Philippine political history, including his memoir Whose Side are We On?, which detailed the events leading up to the declaration of martial law from the perspective of a PMA insider,[13] and his 2005 book The Modern Principalia: the Historical Evolution of the Philippine Ruling Oligarchy.