We can possibly learn from the Bolshevik Revolution in Russias that small adjustments to the economy combined with diplomacy are a way to stave offf wars. Even having said this, it requires good thought, as appeasement in World War II's buildup also didn't work. So it's a combination of Keynesian economics, and diplomacy
If a nation has a bad economy, this will influence its ability to make war. This is the reason why economic sanctions are used to prevent rogue nations from being able to start wars. Economic tools should be used in the future to prevent conflicts and strengthen ties between nations.
Wars are fought 99 percent of the time for economic reasons despite the religious undertones of many conflicts. People impoverished often try to fight their way to prosperity as in the example of Nazi Germany during World War II. If everyone had good jobs and decent housing with enough food, there would be no wars whatsoever.
National wars can be ended through economic changes. Lets face it, the government profits off national wars. It would not be beneficial to our government to end these wars as we must protect our resources on other countries. War as much as we like to believe will not end anytime soon. National wars can be ended if we would stop butting into other countries problems and focus on America for a change.
National wars are fought on many different premises and economics is just one of them. However, economics could certainly help if by that we mean bringing more financial equality to various populations. With more equality there is less oppression and less need for the violent revolution that brings on war.