It’s one of the United States’ best-known rights: automatic citizenship to all born within its borders. But birthright citizenship hasn’t always been the rule of the land in the U.S., and the legal concept has faced plenty of challenges over the century. Here’s the story of birthright citizenship and its challengers.

In the United States, children obtain their citizenship at birth through the legal principle of jus soli (“right of the soil”)—that is, being born on U.S. soil—or jus sanguinis ("right of blood”)—that is, being born to parents who are U.S. citizens.

Most countries in the Western Hemisphere have some form of jus soli citizenship, while Europe favors jus sanguinis citizenship. Today, the United States is one of at least 30 countries that affirm birthright citizenship, including most countries in the Western Hemisphere. “Traditionally” notes the Washington Post, "lenient naturalization laws made it more appealing for Europeans to travel to—and settle in—the New World.”

In 1790, the nation's nation’s first naturalization law came into effect. It stated that “free white persons” could gain citizenship if they had lived in the U.S. for two years and had a good character. The new citizens’ children under the age of 21 were given citizenship, too.

But the new naturalization law ignored massive swaths of American society, including enslaved people and Native Americans, neither of whom were considered citizens.

In 1857, as arguments about slavery roiled, the U.S. Supreme Court went a step further, finding in the Dred Scott v. Sandford case that Scott, an man who had escaped slavery and who was suing for his freedom, was not a citizen because he was of African descent. Nor could any other person of African descent be considered a citizen, even if they were born in the U.S., Chief Justice Roger B. Taney wrote in the majority opinion.

But that definition didn’t last long. During and after the Civil War, lawmakers returned to the debate about whether black people should have birthright citizenship. "What was new in the 1860s...was the possibility for radical legal transformation that accompanied war and its aftermath,” writes historian Martha S. Jones.

In 1864, Attorney General Edward Bates tackled the issue in connection with African American members of the Union Army, finding that “free men of color” born on American soil were American. After the war, the Reconstructionist Congress passed a civil rights law that extended citizenship to all people born in the U.S. who were “not subject to any foreign power.”

The most sweeping declaration of birthright citizenship came in 1868: the Fourteenth Amendment. It defined citizenship as applying to “All persons born or naturalized in the United States, and subject to the jurisdiction thereof.” Notably, due to the "jurisdiction" requirement, most Native Americans were excluded from this amendment.

In 1898, the Fourteenth Amendment’s definition of birthright citizenship met its first major challenge in the form of a Chinese American cook named Wong Kim Ark.

Wong had been born on American soil to Chinese immigrants in 1873, well before the U.S. passed the Chinese Exclusion Act, which prohibited most Chinese immigration and, by extension, the naturalization of Chinese citizens. But since his parents were not citizens, it was unclear whether he too could enjoy birthright citizenship.

When Wong was denied reentry into the U.S. after visiting China, he was forced to wait on a ship in San Francisco harbor for months as his attorney pursued his case for citizenship. He was a test case, selected by the Department of Justice in an attempt to prove that people of Chinese descent weren’t citizens.

His case went all the way to the Supreme Court. Then something unexpected happened: Wong won. “The Fourteenth] Amendment, in clear words and in manifest intent, includes the children born, within the territory of the United States, of all other persons, of whatever race or color, domiciled within the United States,” wrote associate justice Horace Gray in the majority opinion.

Not only was Wong Kim Ark’s claim to citizenship legitimate, Gray wrote, but “To hold that the Fourteenth Amendment of the Constitution excludes from citizenship the children, born in the United States, of citizens or subjects of other countries would be to deny citizenship to thousands of persons of English, Scotch, Irish, German or other European parentage who have always been considered and treated as citizens of the United States.”

To allow a Chinese American man citizenship didn’t threaten white Americans, Gray suggested. Rather, taking his citizenship away would threaten the privilege and citizenship rights enjoyed by white Americans.

The case became precedent and has since been used to defend the birthright citizenship rights of other Americans. In 1943, for example, it was cited (and contested) in Regan v. King, a federal case that challenged Japanese Americans’ right to maintain American citizenship during World War II.

Since then, controversies over birthright citizenship have played out in the court of public opinion. But today, the precedent set by Wong Kim Ark—and the Fourteenth Amendment to the Constitution—still apply.