Europe's generous welfare and pension promises are colliding with a shrinking workforce, and the usual fix — immigration — is itself politically shaky, which is bad news for the continent's long-term growth and good news only for whoever supplies the workers it needs.

• Decades ago European governments promised big pensions and social benefits, assuming a growing young workforce would keep paying for them.
• Birth rates have dropped so there aren't enough workers paying into the system to support retirees pulling money out.
• France stands out, spending about a third of its entire economy on social programs, far more than other rich countries.
• The standard fix has been importing workers through immigration, since the current population isn't having enough kids to do it alone.
• That fix is only a partial patch and brings its own economic and political strains.

Outlook: Unless birth rates recover or immigration policy delivers enough new workers, pressure on European budgets and pension systems is likely to keep building.