Why did the “United States” become a singular noun after the Civil War?

Why did the “United States” become a singular noun after the Civil War? Briefly describe what
you consider the highlights, or the most important aspects of Reconstruction. Cite one or more
events that you believe most affected the future race relations in the United States. Under the
circumstances (given the realities of the day), how might it have been expected to be or could
have been different, considering both what was good about it and that which was unfortunate.
What lesson is there in the attempt to remove Andrew Johnson from office to contemporary
politics?

do NOT include direct quotations  (or
the text, or any other source directly

Why did the “United States” become a singular noun after the Civil War? Briefly describe what
you consider the highlights, or the most important aspects of Reconstruction. Cite one or more
events that you believe most affected the future race relations in the United States. Under the
circumstances (given the realities of the day), how might it have been expected to be or could
have been different, considering both what was good about it and that which was unfortunate.
What lesson is there in the attempt to remove Andrew Johnson from office to contemporary
politics?

do NOT include direct quotations  (or
the text, or any other source directly