One of the most important social movements in the late 19th and early 20th centuries was 'Universal Suffrage' i.e. the right for all adults to vote.
Contrary to popular belief, even in established democracies such as Britain and the United States not every adult could vote in elections.
Women and minorities such as blacks, did not have any democratic say.
Things gradually began to change as more and more countries first allowed women the right to vote and then expanded the law to include all adults in a country.
These changes had, by far, the largest socioeconomic impact on the world in the coming century.