Communism is an idea that says everyone should share things equally so that everyone can have enough to eat, clothing to wear, and homes to live in. Sumatra is a big island in Indonesia where lots of people live.
A long time ago, some people in Sumatra tried to make the country a communist country. They thought that if everyone worked together and shared everything equally, there would be no poor people.
But, the government of Indonesia did not like this idea. They wanted people to have their own money so they could buy what they wanted and not share everything. They said that the communist people were trying to take over the country, so they tried to stop them.
The government was very harsh on the people who wanted communism. They arrested them and put them in jail or even killed them. Many people were afraid to speak up or say they supported communism because they were afraid of what might happen to them.
In the end, communism did not become popular in Sumatra or in Indonesia. Today, people in Sumatra and the rest of Indonesia are free to have their own ideas and beliefs. People can live their lives as they want, but they must also respect the country's laws and customs.