This problem is a principal consequence of major disasters, civil conflict, and war. It may also be associated with some form of ethnic cleansing: active or passive genocide aimed at exterminating a minority culture.
As a consequence of World War II, many children in the UK (whether orphans or not) were separated from their parents under dubious circumstances and despatched to the colonies, supposedly as a form of security. It has been alleged that some ended up working in institutions under conditions approximating those of slave labour.
Indigenous children have been forcibly removed from their families and communities since the very early days of the European occupation of Australia. The findings of the 1997 National Inquiry into the separation of Aboriginal and Torres Strait islander children from their families found that not one indigenous family has escaped the effects. Nationally, the Inquiry concluded that between one in three and one in ten indigenous children were forcibly removed, by the State, from their families and communities between 1910 and 1970.