The population of Aboriginal Australians at the time of permanent European settlement is contentious and has been estimated at between 318,000 and 1,000,000 with the distribution being similar to that of the current Australian population, the majority living in the south-east, centred along the Murray River. A population collapse principally from disease followed European settlement, beginning with a smallpox epidemic spreading three years after the arrival of Europeans. Massacres and frontier conflicts involving European settlers also contributed to depopulation. This violence has been characterised as genocide by some.