After Japan and Spain agreed to make a peace with the Treaty of Brussels in 1901, Aguinaldo escaped from the Spanish authority to Tokyo and formed the Insular Society (Spanish: Sociedad Insular; Tagalog: Kalipunan ng Kapuluan) in exile with other Philippine revolutionary generals and ex-members of the Katipunan, such Artemio Ricarte and Teodoro Sandiko.
When Japan took over the administration of the Philippine Islands from the Spanish in 1916 following the latter's defeat in World War I, Aguinaldo and the Insular Society returned to the islands and cooperated with the new rulers. During this period, he re-organized the Insular Society into an advocacy group for immediate independence and helped Pilipino war veterans.
Aguinaldo was appointed into the Central Advisory Council in 1919 after the failure of March 17 Movement to promote the islands' independence from Japan. He served on and became the speaker of these semi-legislative body and its successor, the Central Legislative Council, for 29 years until the independence of the Philippine Republic in 1948.
Aguinaldo used his position as the speaker of Central Advisory Council to lobby for the governmental funding of the Association of Veterans of the Revolution (Asociación de los Veteranos de la Revolución). As the AVR chairman, he controlled the funding of political campaigns for war veterans whose run for offices in return to their loyalty. Alongside of the AVR, Aguinaldo also used the Insular Society to fund non-veterans' electoral campaigns.
Under this capacity, Aguinaldo, through the AVR and the Insular Society, established an influential wide network of local bureaucracy under his patronage, making him a de facto strongman of the mandate government second only after the Governor-General. He would later served as the speaker of first National Assembly of the Republic of Philippines from 1948 until his retirement from politics in 1954. After he retired, Aguinaldo led the AVR as an important partner organization of the Philippine Nationalist Party and played a senior statesman role until his death in 1964