Population and land

Though more land per person was available in the past than at present, people did not farm all the land available to them for 2 reasons:
(1) people were physically unable to farm larger areas than they actually farmed
(2) farmers in the past had little motive for farming more land

Reduction in the amount of land available to the farmer causes little hardship if previously he was not farming at all the land that was available. When farmers need more land they make more land. People create land--agricultural land--by investing their sweat, blood, money, and ingenuity in it.

Data show that the absolute number of farm workers is going down, and consequently the absolute amount of land per farm worker is going up. 

Job "destruction" is a confusing label for the very essence of economic progress--making a given amount of goods with fewer people. 

In the poorer agricultural countries the creation of new land has been the source of most of the long-run increase in agricultural output which has kept up with population growth. As the available land for crops becomes more and more costly to transform into cropland, farmers will instead crop their existing land more intensively. The use of traditional farmland is no longer the only way to produce food.

The idea that population growth breeds war has been used to justified national policies to "control birth rate". But it doesn't apply in modern society. Additional territory nowadays generally has no value to a nation.