as saudi population grows and oil export revenues stagnate, pressure for "saudization" (the replacement of foreign workers with saudis) has grown, and the saudi government hopes to decrease the number of foreign nationals in the country. saudi arabia expelled 800,000 yemenis in 1990 and 1991 and has built a saudi–yemen barrier against an influx of illegal immigrants and against the smuggling of drugs and weapons. in november 2013, saudi arabia expelled thousands of illegal ethiopian residents from the kingdom. various human rights entities have criticised saudi arabia's handling of the issue. over 500,000 undocumented migrant workers — mostly from somalia, ethiopia, and yemen — have been detained and deported since 2013.