The purpose of Selma to Montogmery march was to raise awareness about the civil rights issues faced by African-Americans. It occurred between March 21-25 in 1965. It was led by Martin Luther King Jr. It led to passage of Voting Rights Act. National Guard of Alabama were called to supervise this march
Remember that at the Constitutional convention, states with large populations clashed with states having small populations. The issue was over representation in Congress.