What really separates the richest town from the poorest one of the European Union?

Wolfsburg (Germany) and Silistra (Bulgaria) are separated by 1,500 kilometers as the crow flies. But prosperity separates them more than distance. Wolfsburg is the richest town in the European Union, the one with the highest income per capita. Silistra is the poorest, the one with the lowest average income. The last Eurostat numbers are quite clear: in Volkswagen’s city you earn more than 140,000 Euros per year (five times the EU average), in the one along the Danube just 3,000. In Wolfsburg the minimum wage for a worker is 2,500 Euros, in Silistra less than 200.