the United States

When you talk about the United States, you have to put "the" in front:

She's from the United States 

There are some cases where you don't use "the" in front, though. Like when you're using "United States" just as a description for something else:

He's a United States citizen.

A few other countries also follow the same pattern:

the Netherlands

the Phillipines

This phrase appears in these lessons: