If you really want to know I suggest this book. But it’s pretty dry reading so let me sum up what I got out of it. Logistics of war have changed a lot and it changes the economics of conquest. Before guns, everything you needed could be supplied from your enemy’s countryside. Conquest was economically useful to the conqueror because you could take your surplus population of single men and feed them and maybe otherwise enrich them at the enemy’s expense instead of your own. But the more stuff you need that can’t be taken directly from nature or from a farm, the more of a supply chain you have to establish. Gunpowder was the first issue. But then guns evolved, and you went from re-using bullets that were just little metal balls that could be picked up from the battlefield and re-used to bullets that had to precision-manufactured to fit a rifled barrel. And on and on. Now you need oil, and modern standards of living mean you have to give the troops better food and housing and medical care, and none of your vehicles or weapons or fancy communication equipment can be replaced by pillaging the countryside. Whatever you get from the damaged country you conquer isn’t going to be as valuable as what you spent to get it.
So if the economics of conquest were to change back in some fundamental way, or the non-economic goals of the actors changed enough to make them able and willing to pay the economic price, then there probably would be more conquest.