What was the Alabama March about?

In 1965, Martin Luther King, Jr. helped organize a march from Selma, Alabama to the state capital in Montgomery, Alabama.  This march was focused on registering southern African Americans to vote.  It took three days for the protesters to march from Selma to Montgomery.  Along the way, they were protected by "federalized National Guard troops."  

In 1964, the Civil Rights Acts changed laws to prevent discrimination for a variety of things, including voting.  Voters could not be discriminated against because of their race.  When organizations tried to register African American voters, they were met with resistance.  Local officials were very much against African Americans registering to vote.  In 1965 in a town near Selma, a large group of people protested peacefully.  This group was attacked.  In the midst of the chaos that followed, a protester was shot by a State Trooper.  After this, King and others organized a march.  They attempted this march twice and were met with resistance.  On the third attempt, they were allowed to proceed.