Her reign, which lasted just over 70 years, saw enormous social and political change across the world.

When Elizabeth II was crowned in 1953, Britain was still a global empire, with world politics increasingly dominated by the confrontation between the U.S. and the Soviet Union.

The queen lived through the end of European colonialism, the Cold War, the rise of China as a new authoritarian power and revolutions in attitudes towards sex, gender and race.

During her reign of more than 70 years the queen met 13 sitting American presidents, stretching from Harry Truman to Joe Biden.

The queen has been succeeded by her 73-year-old son, King Charles III, and Britain has entered 10 days of national mourning.

The Claim

On Thursday Matt Glassman, a senior fellow at Georgetown University’s Government Affairs Institute, claimed Queen Elizabeth II was on the throne for a third of the time the U.S. had existed as an independent state.

He tweeted: “Just a reminder that Queen Elizabeth has reigned for 30% of U.S. history.”

The message went viral, receiving over 11,900 retweets and 100,000 likes.

Glassman later added: “Queen Elizabeth became monarch with Churchill as Prime Minister.

“Churchill was elected MP for the first time in 1900, during Queen Victoria’s reign.

“Queen Victoria was born while George III was still King.

“There’s all of U.S. history, post-British empire.”

The Facts

The United States declared independence from Britain on July 4, 1776, 246 years ago. If this date is used as the starting point for “U.S. history” the queen’s 70-year reign constituted 28.5% of its duration, so between a third and a quarter.

Explaining his reasoning on Twitter, Glassman said he timed U.S. history from the ratification of the American constitution in 1788.

He tweeted: “BTW, the original calculation was done by dividing her reign (since February 1952, 70.5 years) by the time since the ratification of the Constitution (June 1788, 234.17 years). 70.5/234.17 = .302.”

Newsweek checked and Glassman’s calculation is correct.

The Ruling

Needs Context.

As Glassman’s math is right, this one comes down to when you think “U.S. history” began.

If you believe, as he does, it should be measured from the 1788 Constitution ratification, then he’s correct.

However, if you measure it from the signing of the U.S. Declaration of Independence in 1776, as is more conventional, then Queen Elizabeth II only reigned for 28.5% of American history.

FACT CHECK BY NEWSWEEK