Here is Labour peer and happiness economist Lord Layard on the cause of long-term unemployment in Europe:
Europe has a notorious unemployment problem. But if you break down unemployment into short-term (under a year) and long-term, you find that short-term unemployment is almost the same in Europe as in the U.S. – around 4% of the workforce. But in Europe there are another 4% who have been out of work for over a year, compared with almost none in the United States. The most obvious explanation for this is that in the U.S. unemployment benefits run out after 6 months, while in most of Europe they continue for many years or indefinitely.