There are actually two issues here, though they are interrelated.
The first issue is relative military strength. The United States in the relatively same magnitude of military strength as Germany in both WWI and WWII. Nowadays, if we get into a war with other countries, we will usually dominate the airspace and sealanes in relative short order, allowing our forces on the ground much easier opportunities to meet the objectives. The only difficulty comes in the protocols of war in which we reduce civilian casualties as much as possible, which will necessarily increase our own casualty rate. Even so, our casualty rate will be far, far lower than the enemy’s casualty rate.
The second issue is diplomacy, which is two-fold in itself depending on the makeup of the adversary. With dictators, the only ability that works is threat of military force, with actual use of it when necessary. With more advanced governments, favorable win-win trade deals become more likely, with far less likelihood of kinetic operations, aka WWI and WWII redux.
I doubt WWII could have been prevented, at least in scope of world military balances. It is IMPERATIVE that the Constitutionalists ALWAYS have superior, unambiguous military supremacy, to prevent the likelihood of non-suicidal missions of war by adversaries. Otherwise, the temptation is strong. Peace can ONLY be applied through strength. Weakness will ALWAYS bring out the likelihood of kinetic activity.
The key was we had the capability to ramp up and quickly, because we had all the infrastructure in place, with all of the manufacturing plants. We also had plenty of manpower available to make it all happen.