In the context of the United States, the biggest social change since the 1900s has been the introduction of universal suffrage and women and minorities given given the right to vote.
Unlike before, this gave the ability for every adult in the country to choose their representatives and decide on the future of their fate.
It was able to give a voice to millions of people and help further the causes of rights of people.
Universal Suffrage was widely adopted on a Global scale all over the world in the 20th Century and keeps on having an impact in almost every society in the world.