The United Nations Population Fund lists Germany as host to the third-highest number of international migrants worldwide, behind the United States and Saudi Arabia. More than 16 million people are descended from immigrants (first and second generation, including mixed heritage and ethnic German repatriates and their descendants). 96.1% of those reside in western Germany and Berlin. About 7,000,000 of these 16,000,000 are foreign residents, defined as those without German citizenship. The largest ethnic group of non-German origin are the Turkish. Since the 1960s, West and later reunified Germany has attracted immigrants primarily from Southern and Eastern Europe as well as Turkey, many of whom (or their children) have acquired German citizenship over time. While most of these immigrants initially arrived as guest workers, Germany has also been a prime destination for refugees who have applied for asylum in Germany, in part because the German constitution has long had a clause guaranteeing political asylum as a human right; but restrictions over the years have since limited the scope of this guarantee.