effectively, United States of Europe.
Once Europe started on the road to open borders with each other for travel, trade, work and immigration, many were going to come to the conclusion that a common currency makes more sense than 30 different currencies on the continent. (Imagine how much more cumbersome it would be to travel and do business in the US if each state had its own currency.) But having a common currency requires (though it has been largely absent up to now) a common fiscal and economic policy-making structure.
Of course, there is a lot of resistance to this trend in the UK and in many other European countries. It will be interesting to see which path Europe follows: a continuation of the present 'half country (freedom of movement, trade, work and immigration), half-association (sovereign national budgets and fiscal policy); a gradual (or swift) decline in the EU and its eventual disappearance; or a trend towards further integration with the eventual trappings of a national government.
Thanks for posting this, dipsydoodle.