This phase of the war was by far the most costly in terms of civilian loss of life. The combination of warfare, famine and plague caused a huge mortality among the Irish population. William Petty estimated (in the 1655–56 Down Survey) that the death toll of the wars in Ireland since 1641 was over 618,000 people, or about 40% of the country's pre-war population. Of these, he estimated that over 400,000 were Catholics, 167,000 killed directly by war or famine, and the remainder by war-related disease. Modern estimates put the toll at closer to 20%.