I fully agree that the use of military force should be completely outlawed, and not only that for territorial gain you mention, since Russia and the USA both use force as political policy enforcement.
But sadly that is the theory and impossible for the following reasons:
1) THe USA has set itself and NATO as an unauthorised international police force by force alone, which given the USA's appalling record of war crimes (Napalm, Agent Orange, Carpet Bombing, Shock and Awe Attack, Multiple Illegal Invasions, Regime Changes, Promoting dictatorship) makes it totally unacceptable for performing that function to much of the world.
2) The United Nations should be the deciding and enforcing body, but it was emasculated when it was first set up by the USA who refused to let the rest of the world set it up in neutral Switzerland and also insisted on the right of veto by a small select band of powerful permanent members, China, France, Russia, United Kingdom, United States.
In other words, the bullies in charge of the playground.
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