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Thomas Malthus was an English clergyman who, in 1798, published an Essay on the Principles of Population in which he put forward the view that, "the power of population is indefinitely greater than the power of the earth to produce subsistence for man." He thought that a balance could only be maintained if famine, disease or war periodically increased the death rate and reduced population growth. His pessimistic ideas were accepted by several other 19th century scholars in England and France. At the end of the 19th century, the population of England was only about 10 million, but much of their food supply had to be produced from the limited agricultural land of the country. Changes in land tenure, brought about by enclosure of the old common fields and the formation of large farms in the place of small scattered plots led to rural depopulation. The towns, especially those where the new factory industries had been established, grew very rapidly and were overcrowded, dirty and unhealthy. The people who lived in them were poor, under-fed, overworked and had little resistance to disease. Thus, had food supply been reduced or population expanded too rapidly, these people would have suffered starvation and epidemics would have reduced the population. This has already happened twice during England's history; the Black Death of fourteenth century and the Great Plague of the seventeenth century coincided with periods when harvest was bad and there were food shortages. Hunger reduced resistance to diseases and bubonic plague caused the death of many thousands of people. Malthus was afraid that something similar would happen again. In his time, great advances were being made in the treatment and control of diseases such as cholera, typhoid and smallpox which were still rife in England and Europe. This meant that death rates, and particularly infant mortality rates, were falling. Malthus calculated that population could double every twenty-five years, but no similar increases in food supplies could be expected.He could not have foreseen the tremendous changes which were to take place in the nineteenth and twentieth century.