Question

Why might a balance of power prevent war?

Answer 1

Not that there is such a thing as a BALANCE power [and control]...Don't think such a thing exists. a balance of power, is almost a delusion. Just there to make people believe it really is balanced, when really, it isn't. 
A balance of power, will distribute power [and control] evenly, to both the civilians and podiums stakes. If it weren't for, lets say democracy, the podium holders will get everything. Think about what Augustus Caesar did, to obtain power. He created the illusion of a balance of power, when it really was a dictatorship...He played the puppet master. War wasn't prevented, even with that illusion...But Ig looking at today's advanced society, the moral reason would be that a balance of power, i.e. democracy, may just be the key to avoiding war. For example, many Americans, feel that they should wage war against Iran and Iran. But, the government, feels its non strategic and stupidity. So that kinda balances it out.

Hope this makes sense...Also, I answered your other question about a balance of power. :) Chur

Answer 2

Without a balance of power one branch of government or a person might become to powerful and the country would become a dictatorship. People now and days fight against dictators and prevent war.