Thousands of people have marched in South Africa's main cities to demand that all undocumented migrants leave the country. Police officers - backed by private security guards - have been deployed because of fears that protests could turn violent. Anti-migrant groups had set Tuesday as the deadline for undocumented migrants to leave. Many foreigners have already fled to escape violence and intimidation. South African police say 25,000 have been repatriated so far. Most are from other African countries. One undocumented Malawian told the BBC he was "happy to be going back" but "heartbroken" to be leaving behind four young children....