Christian Filipino legislators in the bicameral US civil administration played a hitherto unacknowledged role in pushing for the colonisation of Mindanao, as part of the Philippines, by proposing a series of Assembly bills (between 1907 to 1913) aimed at establishing migrant farming colonies on Mindanao. This legislative process was fuelled by anger over the unequal power relations between the Filipino-dominated Assembly and the American-dominated Commission, as well as rivalry between resident Christian Filipino leaders versus the American military government, business interests and some Muslim datus in Mindanao itself for control over its land and resources. Focusing on the motives and intentions of the bills' drafters, this study concludes that despite it being a Spanish legacy, the Christian Filipino elite's territorial map — emphasising the integrity of a nation comprising Luzon, the Visayas and Mindanao — provided the basis for their claim of Philippine sovereignty over Mindanao.