The difference between the quality of the infrastructure (esp. roads and rail) in the Netherlands and Belgium must surely be the most convincing testament to what a country loses from even relatively mild (from a worldwide point-of-view) levels of interethnic squabbling!
It's not just that, it's also a conceptual difference. Belgium is a tax haven compared to the Netherlands and there are whole towns made up of rich Dutch tax evaders just across the border. Less taxes, less money for infrastructure.
Funnily enough the Netherlands is also a tax haven but it's only for large megacorporations, not people. They wouldn't be based there at all if it wasn't for the tax benefits so they don't lose out by offering it, they just screw the rest of Europe over by allowing companies to evade taxes in the whole EU.
