Can you imagine a future whereby nations agree to an alternative to war? Disputes may never go away, but the resolution mechanisms might change. The mechanism's effect would have to be quite similar to the forgone war's would-be effect for both nations to agree.
Presumably, some wars happen when each side believes it would win even though they both cannot
be correct. The inputs would be the quantities of soldiers, armaments, ammunition, technology, etc. Who has the higher total? Now, go back one step: who has an economy capable of generating more of these inputs? Now, go back another step: who has a society that is more conducive to having superior economic output (think productivity, raw materials, skills, incentives)? Effectively, the better equipped social system is likely to be the eventual winner. So, how to simulate this without bloodshed?
Allow countries to buy parts of territories adjacent to its borders; similarly, countries could pledge its own adjacent land as collateral when borrowing money. This needs much more thought, but could have some interesting outcomes.