It is from Crash Course US history. It is at 8 minute and 10 second. Here is the contex:
Taney ruled that black people "had for more than a century before been regarded as beings of an inferior order...".
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The issue with the tense comes from the use of quotations marks where there should not be any, as this is a statement of his words rather than an exact quote.
Taney ruled that black people had for more than a century before been regarded as beings of an inferior order...
This sentence states what Taney ruled at some time in the past. At that time, he ruled that they had been regarded as inferior. If this was indeed an exact quote, the tense of the verb would have to change, such as:
Taney ruled, "Black people have for more then a century been regarded as inferior."