President Johnson's Voting Rights Act Speech

Read the following excerpt and answer the question that follows. there is no constitutional issue here the command of the Constitution is plain there is no moral issue it is wrong deadly wrong to deny any of your fellow Americans the right to vote in this country there is no issue of states rights or national rights there is only the struggle for human rights I have not the slightest doubt what will be your answer but the last time a president sent a civil rights bill to the Congress it contained a provision to protect voting rights in federal elections that civil rights bill was passed after eight long months of debate and when that bill came to my desk from the Congress for my signature the heart of the voting provision had been eliminated this time on this issue there must be no delay or no hesitation our no compromise with our purpose we cannot we must not refuse to protect the right of every Americans to vote in every election that he may desire to participate in and we ought not and we cannot and we must not wait another eight months before we get a bill we have already waited a hundred years and more and the time for waiting is gone so I asked you to join me in working long hours nights and weekends if necessary to pass this bill and I don't make that request lightly far from the window where I sit with the problems of our country I recognize that from outside this chamber is the outraged conscience of a nation the grave concern of many nations and the harsh judgment of history on our acts but even if we pass this bill the battle will not be over what happened in Selma is part of a far larger movement which reaches into every section and state of America it is the effort of American Negroes to secure for themselves the full blessings of American life their cause must be our cause - because it's not just Negroes but really it's all of us who must overcome the crippling legacy of bigotry and injustice and we shall overcome

Based on the information presented in the excerpt, what event or discriminating practices motivated President Johnson to address Congress about providing federal protection for the rights of African Americans and other minorities to vote?