Deutsche Bank Chief Economist David Folkerts-Landau told Die Welt last month. “I could even imagine a cultural and economic renaissance.”

Downvoters: you really hate to see facts that don't fit your preconceptions, eh?

They have to leave when their homeland is some sort of stable.

Ibn Khaldun uses the term Asabiyyah to describe the bond of cohesion among humans in a group forming community. The bond, Asabiyyah, exists at any level of civilization, from nomadic society to states and empires.[3] Asabiyyah is most strong in the nomadic phase, and decreases as civilization advances.[3] As this Asabiyyah declines, another more compelling Asabiyyah may take its place; thus, civilizations rise and fall, and history describes these cycles of Asabiyyah as they play out.[3]

Ibn Khaldun argues that each dynasty (or civilization) has within itself the seeds of its own downfall. He explains that ruling houses tend to emerge on the peripheries of great empires and use the much stronger `asabiyya present in those areas to their advantage, in order to bring about a change in leadership. This implies that the new rulers are at first considered "barbarians" by comparison to the old ones. As they establish themselves at the center of their empire, they become increasingly lax, less coordinated, disciplined and watchful, and more concerned with maintaining their new power and lifestyle at the centre of the empire—i.e, their internal cohesion and ties to the original peripheral group, the asabiyya, dissolves into factionalism and individualism, diminishing their capacity as a political unit.