Probably because they were murdered.
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Answer:
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Explanation:
It is this line: "<span>Fellow-citizens, above your national, tumultuous joy, I hear the mournful wail of millions! whose chains, heavy and grievous yesterday, are, to-day, rendered more intolerable by the jubilee shouts that reach them."
Douglass admits that the Independence Day is an important date when a great thing happened for all Americans. But he thinks it is inappropriate to celebrate a nationwide holiday when there are millions of members of this nation who are not free and able to celebrate. This festivity makes those people feel even worse.</span>
Adventures of Huckleberry Finn and The Prince & the Pauper