Okay kiddo, do you know what immigration is? It's when people from one country move to another country to live there. The Immigration Restriction League was a group of people in the United States who wanted to make it harder for certain types of people to come to America.
They believed that some people were not good for the country, and that letting too many people from certain countries into America would hurt the country's economy and culture. They wanted to limit the number of people who could come to America, and they especially wanted to keep out people from certain countries like China and Japan.
But, not everyone agreed with them. Some people thought that America was a country of immigrants, and that everyone should have the chance to come and live here if they wanted to. So, there were a lot of arguments and debates about what the Immigration Restriction League was trying to do. In the end, some of their ideas were put into laws, but many people still immigrated to America and today, the U.S. still continues to be a nation built by people from all over the world.