From Der Spiegel: High-Speed Trains Erode Europe's Borders.
The Eurostar now carries more than 70 percent of passenger traffic between London and Paris. And air service between Paris and Brussels has ended altogether now that trains connect those cities in 1 hour and 20 minutes.
It's faster (and cheaper, despite the dollar) to ride coach from London to Paris than from New York to Washington. And Europe's Railteam is making it easier to cross national borders and switch between rail systems, with the goal of seamless travel from Paris to Bratislava.
This, more than a common currency or labor market, could make Europe Europe.