For example, in both Canada and Australia, there's no history of institutionalised slavery

If only that was true in Australia. But alas, not so much (http://en.wikipedia.org/wiki/Blackbirding).

I went to school with descendents of indentured pacific island workers. It's still a matter of dispute as if it was slavery, I mean, it wasn't anything like Gone with the Wind, plantation style, in numbers or trade. But it happened.