Phony respect for "Aboriginal Elders", page-25

Less than 200 Spanish soldiers invaded the Inca empire, which at the time had up to 14 million people. Out of 14m, they had something like 80k soldiers.

However once their King was killed, their political organisation was lost and the entire empire fell into disarray. Aboriginals had up to 1m people but lacked organisation.

Britain determined 247 soldiers was enough to meet the resistance of the local Eora people based on prior survey of Botany Bay from Captain Cook. The first fleet also had 2 Navy vessels specifically for combat.