Forced labour covers a wide range of practices, from slavery to compulsory national service of a military or civil kind. Its effect varies from the total subjugation of prisoners, particularly political prisoners or prisoners-of-war, and of slaves, to the hardships endured by people recruited for national service. It may have severe adverse physical effects especially in the case of the two former. Forced labour associated with malnutrition and crippling diseases has led to the death of millions.
IG Farben, Germany's largest chemical cartel, employed slave labor to build its synthetic rubber factory to supply the Nazi war machine, and treated slave workers brutally - those too sick to work at breakneck pace were killed with the company's Zyklon B gas in gas chambers. After the war, some Farben officials were convicted of crimes against humanity along with government officers at the Nuremberg Trials.
The Global Slavery Index 2013 found just under 30 million incidences of modern slavery, worldwide.
Compulsory military service prevails in many industrialized countries, whereas other compulsory services are often exacted by law in developing countries. Prison labour is closely connected with forced labour but is given special consideration under the UN Forced Labour Convention. Labour may be imposed on persons awaiting trials, or as a means of punishment, or prisoners may be contracted out to private employers. Forced labour of political prisoners is known to be practised, but governments are reluctant to admit this or give information. The forced labour in Nazi concentration camps and its horrible conditions were not realized by the world until they were in existence almost ten years. However the tragedy of forced labour in the former Soviet Union, particularly in the Gulag, has been exposed by a number of persons who have been interned there. Forced labour was legal in the racially segregated system of South Africa, involving the exploitation of cheap African labour which was usually housed, fed and paid inadequately, segregated by sex and restricted in movement. The practice also occurs illegally in Latin America where Indians are enslaved and for Mexican migrants in the south-western USA.
Immigrants into western European countries recruited from Africa, the Middle East and Asia for menial work in factories find themselves excluded from unions and therefore unable to bargain for better conditions. Inadequately housed and unable to bring their families to live with them, they have to continue working under poor conditions because of the need to support their families.