Which of the various theories of migration seem best able to explain patterns of migration within, to, and/or from Germany and Yemen?

Good resources include the Migration Dialogue at UC Davis at http://migration.ucdavis.edu, the Migration Policy Institute at http://www.migrationpolicy.org/programs/migration-information-source, the United Nations’ International Labour Organization at http://www.ilo.org/global/lang–en/index.htm, the United Nations High Commissioner for Refugees at http://www.unhcr.org/cgi-bin/texis/vtx/home, and the United Nations Population Division at http://www.un.org/en/development/desa/population/theme/international-migration/index.shtml

just 1 paper is enough!