Question

How do you think the historical denial of voting rights to african americans affected the makeup of congress and many state legislatures?

Answer 1

If your skin is purple and purple people are not allowed to vote, it's likely your elected officials would not pay much attention to issues that are important to purple people, right? And you wouldn't find purple people in Congress or state legislatures either. OK now change skin color from purple to black. You will see that for many many years, Congress and many state legislatures were mostly (if not entirely) white males. 
White men of the 18th and 19th centuries already had their rights and so the civil rights movement as we know it today didn't exist back then. It was only when blacks and women gained the rights to be educated and to vote in the late 1800s and early 1900s that the civil rights movement began to take hold and by the 1960s there was a flood of civil rights legislation being signed into law. You will also note that this happened as more blacks and women got elected to Congress and state legislatures.