Malthusian checks could be positive or preventive, and they might operate simultaneously. The basic idea of the positive check was that a rise in population would tend to lead to a rise in food prices and hence a fall in real income. There is a limit to what both labour and capital productivity increases can accomplish and so eventually the food supply would run out, and mortality would ensue. The population would fall and real incomes rise, and the cycle would start again. The preventive check was the decision by people not to marry when economic resources were scarce, which would stop a surge of population. Where the preventive check operated nuptiality would eventually reach an equilibrium balance between resources and population, although real wages would be less than they might be.
The preventive check seems to have operated throughout much of Europe in the pre-industrial period. It is ironic that only as Malthus was writing in 1798 was the system starting to break down, at least in England (we have very definite evidence on this at least). The European demographic system was predicated on small administrative and economic units in which there existed a fixed amount of holdings - be they land holdings or trading opportunities. The nuptiality of the young therefore depended on "dead men's shoes" - people would marry and set up a household when they inherited a particular trade position or piece of land. In this way economic resources were allocated to couples who could then support a family with them. This preventive check stopped huge population growth of the sort that occured in England in the 18th century.
In England, the focus was less on a communal means of support - the demographic system was more individualistic. The delay before marriage was more to do with the personal accumulation of wealth, usually from a position as a live-in servant-in-husbandry or perhaps in a trade. Once people had enough wealth saved up they would move into a house and marry - and in England this was, until the mid-18th century, usually when they were between the ages of 25 and 30. Another important factor was their perception of the economic viability of their household in the future - if they expected their job to dissapear in a few years they would not marry. Thus stable economic conditions for a long period would lead to earlier marriage, but bad economic conditions would tend to discourage people from marrying altogether.
Through these preventive checks Europe largely avoided the ravages of the positive check, when Nature audited with a red pencil. Malthus also talked about other positive checks, such as disease - and indeed, the microbiological world did affect our human one greatly. England suffered no major mortality crises with over 20% of the population dying after the reign of Elizabeth I, as well as doing away with famine earlier than most places (France had a subsistence crisis in 1817). Increased urbanisation in the early modern period (particularly marked in England) led to increased mortality initially - London, for instance, absorbed half the English population growth in the seventeenth and eighteenth centuries. Advances in healthcare, housing and welfare spending would eventually remove the status of the cities as "devourers of the population".
The manner in which England did away with the subsistence problem - through centralising agriculture and increasing its productivity - is now seen as the factor which stopped the English system being Malthusian. The proletarianization of the English work force moved England even further away from the European model of demographic control. As more people entered the social group of wage labourers, they were encouraged to marry earlier - they no longer anticipated being landowners themselves in the future, nor being live-in labourers, and so reached the peak of their earnings earlier in their lives. The rise of so-called "proto-industry" - usually performed in people's own homes - encouraged population growth in two ways. Firstly, children were an economic asset and therefore people were more likely to regard their household's future as rosy if they had children. Secondly, because the products were often exported or at least sent outside the current economic environment, people tended to view the stability of their work more favourably.
Malthus' predictions about the future turned out to be incorrect - as agriculture was made increasingly productive the chance of famine destroying the system due to endogenous factors lessened. His description of the system that operated in early modern England was largely correct, however - although he also thought that population growth was encouraged by the Old Poor Law, which parish studies have shown it wasn't. Only when industrialisation began and humanity moved onto a new plain of scientific and technological development could periodic famines be resigned to history, rather than being the lot of all men.