The 19th century, at a universal scale, continues the cycle opened at the end of the previous century with changes of vital importance. This allows us to call this stage, at least until the middle of the century, the era of revolutions.
These changes are reflected primarily in the number of inhabitants. The world population grew between 1750 and 1850 as much as in the previous thousand years. The first leap forward of the world population starts especially in Europe, which passes from nearly 200 million inhabitants in 1800 to 400 million in 1900, providing an abundant labour force for its industry and a much larger market of consumers for its industrial products.
This “demographic revolution” is the result, as we have seen in the 18th century, of the changing behaviour patterns of the ancient demographic regime, attending, since the middle of this century in Britain, and in most of Europe throughout the 19th century, to a systematic decrease in mortality (for example, in England it decreased from 26.9 per thousand in 1800 to 18.2 in 1900), while the birth rate remained at a high level at least until the end of the period, resulting in an extraordinary population growth.
All these developments have to be related, first, with the improvements in agriculture that allow to expand and diversify the diet, giving organisms greater resistance to disease and secondly, with advances in medicine (the discovery of the smallpox vaccine; the birth of microbiology;
the introduction of partial anaesthesia and antisepsis in surgery) and health (drinking water in cities, the cleaning of the streets and the widespread use of personal hygiene with the use of underwear and soap). However, this did not prevent the continuation of some features of the old demographic regime: the infant mortality rate did not descend until the last quarter of the century, the "famines" did not disappear systematically (Ireland 1846 -1848) and some epidemics such as cholera, which made its debut in Europe in 1832, continued to plague the continent.
