What motivated the founding fathers to include the phrase "to form a more perfect union" in the preamble of the u. s. constitution?

One of the main things that motivated the Founding Fathers to include the phrase "to form a more perfect union" in the Preamble of the U.S. Constitution is because they knew that things like slavery and other impaired citizens rights would have to be eliminated someday. 

The answer to your question would be b