America started doing so at the end of the Civil War. The constitution was amended then to overturn the Dred Scott decision of 1857, which held that black people were not Americans. The 14th Amendment ensured that freed slaves and their children would henceforth be citizens.

"When I heard that President Trump signed an Executive Order that would deny my child United States citizenship, my world fell apart," one woman wrote.

Here's a guide to what birthright citizenship is, what happens if Trump's order ends it, and what comes next after lawsuits were filed.