In the case of France, it took about 100 years after the French Revolution broke out to really get a republican-style system of government (Third Republic) the original revolutionaries wanted. I don't think you and others would have wanted to live through Robespierre's Reign of Terror where thousands of killed sometimes for "looking like a criminal" i.e. thought-crimes, "counter-revolutionaries", drowned in mass barges, mass shootings in front of adoring, cheering crowds, guillotining innocent French men, women and children and then allowing an enlightened depsot to take power who was territorially aggressive who set France at war with all of Europe for the next 25 years.
A lot of unnecessary dead bodies had to pile up to reach a more democratic France. You mention the 13th Amendment here in the U.S, well it took a century and several landmark SCOTUS cases along with a twenty year legal, political and sometimes police actions to force many Deep South states to end state-enforced segregation laws in schools, hospitals, private and public employment/institutions. Their were countless threats, bombings, public and private attacks on civil rights activists, organizations outside of bus stations, supermarkets, homes, businesses that made the process of desegregation/integration harder.
In the case of apartheid South Africa: yes, Apartheid is gone but SA still remains a deeply flawed, corrupt, extremely violent country and society in some respects and although Nelson Mandela was a great leader, many of his ANC heirs have not shown his same honesty, candidness, openness, and drive for a truly more racially-equal and just South Africa. Are they better then post-colonial Zimbabwe, Angola, or Mozambique? Sure, but those aren't exactly high bars of excellence to surpass.
And sometimes, you don't get a more democratic nation? You get the IRA/Sinn Fein, Red Guards, Belder-Meinhof Gang in West Germany from the late 60's-80's bombing, killing U.S. troops, kidnapping West German businessman and then killing them because they hate consumerism too much or _____ murdered person's parents were Nazis or former Wehrmacht/Waffen-SS soldiers.