What did Osama Bin Laden mean by "eighty years of humiliation?"

Osama Bin Laden made two references to "80 years." The first: "What America is tasting now is only a copy of what we have tasted. Our Islamic nation has been tasting the same for more than 80 years, of humiliation and disgrace, its sons killed and their blood spilled, its sanctities desecrated." Later, Osama repeated the temporal reference, saying "the sword fell upon America after 80 years."