Too much land makes its defence is onerous, its cultivation inadequate, and its yield surplus, which causes defensive wars. If there is not enough land, the state is at the discretion of its neighbours for what it needs as surplus, causing offensive wars.
Gist of Idea
Too much land is a struggle, producing defensive war; too little makes dependence, and offensive war
Jean-Jacques Rousseau (The Social Contract (tr Cress) , II.10)
This sounds much too simplistic, like the causes of squabbles in a kindergarten. Certainly inequalities between nations (such as the USA and Mexico) produces frictions. Advances in agriculture technology have transformed this problem.
Rousseau,Jean-Jacques: 'The Basic Political Writings', ed/tr. Cress,Donald A. [Hackett 1987], p.168