Three things that cement a man's claim to land: improving the land, building a family, planting and harvesting crops. These things are as much a part of the process of filling and subduing the land as evicting Canaanites.

A man can be exempted from war if he has recently planted a field, but has not yet harvested it for himself. Depending on the crop, this exemption could last as long as five years.

Deuteronomy 20:5-7