<span>United States, United Kingdom and the Commonwealth, Soviet Union, Republic of China, Poland, France, Yugoslavia
</span>
Explanation:
Slavery, condition in which one human being was owned by another. ... a perceived labour shortage, for otherwise it is unlikely that most people would bother to acquire or to keep slaves.
I think your answer should be either the third choice or second choice. They both make sense to me but the other two are definitely not it. Hope this helps! =^-^=
