Shays' Rebellion was a big problem that happened a long time ago in the United States (in the late 1700s). It was named after a guy named Daniel Shays. Basically, a lot of farmers in Massachusetts were having a really hard time paying their taxes and debts because of a lot of big problems going on in the economy. They were very unhappy with the government at the time because they didn't think they were being treated fairly.
So, a group of farmers decided to rebel against the government. They got together and started a big fight with the government officials, and they even tried to take over a courthouse. But the government didn't like that, and they sent troops to stop them.
In the end, the rebellion didn't really work. The farmers were defeated and lots of people got hurt. However, the event ended up being really important because it showed that many people in the country were really unhappy with the way things were going. It helped lead to some big changes in the way the government was set up, so that the people would feel more included and better taken care of.