Records from this period begin to coincide with the infancy of the science of human statistics, or demography. Parish registers were now to be kept more thoroughly and on their basis the first total figures of births, marriages and deaths were calculated. States began to organize their first census returns during the eighteenth century, although for very pragmatic purposes, such as to calculate poll-taxes and military service. Methods were never standardized, and lack of staff invariably meant that the census was incomplete. Population policy was part of power politics, but the most powerful state of all, Britain, conducted no census before the nineteenth century. One is thus still dependent on estimates, as in the sixteenth century, athough these are now far more accurate.
Church registers of births and deaths, estate records, land tax and hearth tax registers, poll-tax lists and musters to arms provide essential population records. Interpretation is difficult but according to recent calculations, Europe had 100 million inhabitants in 1600, 140 million in 1700 and 188 million in 1800. These totals do, however, hide great regional variations in growth.
The effects of war on population in the seventeenth century are still hotly disputed. Central to the debate is the question of population loss in Thirty Years' War in Germany. Loss remains a vague term, and displacement of population by movement from one region to another is probably a more realistic approach than outright devastation. It is too early to say what overall population displacement had taken place in Germany by the I64Os. Calculations of the losses are between 30 and 40 per cent, and it is thought that it took about three generations to reach again the figure of twenty million. Industrial and commercial expansion of certain centres stimulated by the needs of warfare