I’ve recently come across the ‘golden arches theory’ – No two countries with a McDonalds restaurant have ever gone to war with each other. It was shorthand for saying globalisation and strong economic ties reduce conflict.
This theory was espoused by Thomas Friedman in a book The Lexus and the Olive Tree published in 1999. Although this theory is not quite true (Nato bombing Serbia, Israel vs. Palestine, more recently Russia and Georgia), it emphasises his point that countries which trade with each other are more likely to want to stay friends, as their exports and imports depend on it. An interesting theory.