If you think of the question in other terms, perhaps it will come clear to you. Dissenters in the Soviet Union had inalienable rights, but the government imprisoned them, so their rights were figuratively taken away. In this case, they knew they had rights and they knew they had had their rights removed from them: they were imprisoned. In another scenario, a baby born in a famine area, maybe Darfur, has an inalienable right to food and life and liberty. The baby doesn't know this however. If the baby doesn't get nourishment for a healthy life, you might say her/is rights are taken away by famine, war and government. Perhaps a better phrase is "violated": her/is inalienable rights are violated. This would apply to both examples.
In the original example of Europeans and Americans taking Africans as slaves, perhaps (perhaps not ...) it will help to clear things up by approaching it this way. African tribal members didn't read Western philosophers. It was Western philosophers who spoke of inalienable rights. The Africans wouldn't know about their "inalienable rights" any more than the baby would know about her/is inalienable right to food and life. The African tribal members did however know about their sense of human dignity, human value, human worth, respect, honor, etc. This can be confirmed by reading works like Things Fall Apart.
When Africans were confined in slavery, the captors were violating--ignoring, wronging, disrespecting--the Africans' dignity, respect, humanity, value, worth, honor. The captors were treating Africans like horses they might round up to take to America to auction off for farm labor. It is in this way that Africans' philosophically articulated inalienable rights were violated, dishonored, and figuratively "taken away." In truth, their inalienable human rights remained inalienable even though the rights were trampled upon (like the baby being left with no food or care), imprisoned (like the political dissenters), disrespected, dishonored and abused. This would equally apply to your example about women's rights.
In this scenario you are wrestling with, inalienable (that which cannot be taken away or removed) means that no matter how Africans were treated and mistreated--they remained dignified humans with undiminished worth and value who deserved lovingkindness, respect and honor. They maintained their dignity and humanity: a human being's dignity and humanity does not depend on what others believe or do, it depends wholly upon the condition of being human. This explains the necessity of the captors' developing the theory that African slaves were not truly human: by this egregious theory, the captivity and abuses African slaves received did not really matter because, in the eyes of the captors, they were not truly human and therefore had no rights.