The invention of agriculture didn’t end the struggle for food. Early agriculture was a much harder way of life than hunting and gathering at the time. The first agriculturist peoples were severely malnourished compared to their h-g neighbours. They had a very poor diet of limited variety, and a lot less available meat.

Early agriculturists were also easy pickings for hunter gatherers to raid their food stores and plunder everything. Between the poor soil, poor variety of crops, poor nutrition and low protein, infestations of mould and vermin, and constant attacks by raiders, life for these folks was an extreme struggle.

Looking at that situation, it should be a lot easier to see why agriculturalist societies soon developed militaries and became warlike. And why local lords demanding 2/3 of your produce was a fair trade for having a military that would drive its enemies hundreds of miles away from your farm.