Norway's Nobel Committee handed its 2012 Peace Prize to the European Union, even as the bloc faces its most serious crisis since it emerged from the ruins of two world wars, an award that served as both endorsement and warning.

The committee, whose decision Europeans both celebrated and mocked, said the prize recognized more than six decades during which the conflict-ridden continent pulled together and became a harbinger of "peace and reconciliation, democracy and human rights" at home and beyond....