As usual in wars of this era, disease caused more deaths than combat. There are no accurate figures for these periods, and it is not possible to give a precise overall figure for those killed in battle, as opposed to those who died from disease, or even from a natural decline in population.
Figures for casualties during this period are unreliable, but some attempt has been made to provide rough estimates. In England, a conservative estimate is that roughly 100,000 people died from war-related disease during the three civil wars. Historical records count 84,830 dead from the wars themselves. Counting in accidents and the two Bishops' wars, an estimate of 190,000 dead is achieved, out of a total population of about five million.
Figures for Scotland are more unreliable and should be treated with greater caution. Casualties include the deaths of prisoners-of-war in conditions that accelerated their deaths, with estimates of 10,000 prisoners not surviving or not returning home (8,000 captured during and immediately after the Battle of Worcester were deported to New England, Bermuda and the West Indies to work for landowners as indentured labourers). There are no figures to calculate how many died from war-related diseases, but if the same ratio of disease to battle deaths from English figures is applied to the Scottish figures, a not unreasonable estimate of 60,000 people is achieved, from a population of about one million.
Figures for Ireland are described as "miracles of conjecture". Certainly the devastation inflicted on Ireland was unbelievable, with the best estimate provided by Sir William Petty, the father of English demography. Petty estimates that 112,000 Protestants were killed through plague, war and famine, and that 504,000 Catholics were killed, giving an estimated total of 618,000 dead, from a pre-war population of about one and a half million. Although Petty's figures are the best available, they are still acknowledged as being tentative; they do not include the estimate of 40,000 driven into exile, some of whom served as soldiers in European continental armies, while others were sold as indentured servants to New England and the West Indies. Many of those sold to landowners in New England eventually prospered, but many of those sold to landowners in the West Indies were worked to death.
These estimates indicate that England suffered a 3.7% loss of population, Scotland a loss of 6%, while Ireland suffered a loss of 41% of its population. Putting these numbers into the context of other catastrophes helps to understand the devastation to Ireland in particular. The Great Hunger of 1845–1852 resulted in a loss of 16% of the population, while during the Second World War the population of the Soviet Union fell by 16%.
Read more about this topic: English Civil War