International conflict is avoided when two enemies have equal capacity to inflict damage. When one enemy acquires better equipment, better trained or more combatants or has some other clear advantage the situation can quickly degenerate into war.
As any military historian knows, fighting and winning a war is a nearly infinitely complex task. The motivation of troops, their training, the skills and integrity of the officers, the reliability of intelligence and how it is used, where battles are fought and in what weather even the time of day, logistics, propaganda and weapons all play important roles. To equate, weapons parity with military balance is naive.