Okay kiddo, so a looong time ago in the year 1705, some people in England were worried about foreigners coming into their country. These foreigners were sometimes called "aliens", even though they weren't really from outer space.
Now, those people who were worried convinced the government to pass a law called the Alien Act. What did that law say? Well, it said that any foreigner who wanted to live in England had to get permission from the government first. And if they didn't get permission, they could be kicked out of the country!
This was pretty mean, right? But there were some people who were okay with it because they thought it would help keep England safe from bad guys.
Overall, the Alien Act wasn't a very nice thing to do. We should always remember to treat people from other countries with kindness and respect, no matter where they come from.