GDP is a good measure of economies. After the war Europe had a lot of catch up growth and was increasing relative to the U.S. In the last ten years European countries have been declining and more problems are coming in the future. To mention some
1. Fall in their ability to compete and outsourcing
2. Low birthrates, (1.3 in Germany, Italy, Spain, Greece, etc.) and the aging of the population
3. Immigration isn't working at all. Just look at what Switzerland forbid a week ago. Also, immigrants have a higher tendency to be on welfare programs, and work less. The number of immigrants are increasing fast, very fast.
4. Work ethics are declining and number of hours worked have been declining.
5. Number of years in workforce is also declining.
6. People are not willing to change and think more socialism is the solution.
7. Taxes are already high in most European countries, and higher taxes will hurt their economies.
Germany, France have had a growth rate of 1.5%, the last ten years. Italy 1.0%. Spain has an unemployment of 20%. U.S. has high unemployment now (10%), but it is mostly demand-deficient and will improve a lot in better times. Most European countries have a lot of structural unemployment. Just look at how high their unemployment was before the crisis. Of the big countries, only U.K. seem to do fine, but U.K. isn't a left-wing country.