London was pretty dense when the black death reduced the population. Disease had not prevented it from reaching that density.

A problem of more land under cultivation is food transport.

Another mechanism of population control is warfare. A predisposition for war, and conquest of land, avoided food shortages in the first place - for the victors. In short: the Four Horsemen of the Apocalypse maintained carrying capacity. Another, rarely practiced, was infanticide.

This is increasingly being solved with contraceptives. Note that TV, internet, video games, wealth and education have contraceptive effect.