Of all the things that could inflame tensions in a region that could someday be a theater of war between superpowers, the movie “Barbie” was not an obvious catalyst. Yet here we are.

The authorities in Vietnam this week banned the upcoming Greta Gerwig film over a map in “Barbie” that they said shows a Chinese map of territory in the South China Sea, where the two neighbors have competing claims.

The Philippines, another Southeast Asian country that disputes China’s territorial claims in the sea, is now deciding whether to ban the star-studded film as well. And Vietnam said on Thursday that it was investigating a South China Sea map on the website of a company promoting Blackpink, a K-pop band scheduled to perform in Hanoi this month.

Taking such stands against seemingly innocuous cultural exports may look to some like an overreaction. But Vietnam’s responses make more sense if they are viewed within historical and political contexts. Here’s a primer.

What is Vietnam’s beef with ‘Barbie’?

The head of the Vietnam Cinema Department, an agency in the one-party state, said on Monday that the Warner Bros. film would not be released domestically because of a scene that includes the so-called nine-dash line — a map that appears on official Chinese documents and encircles most of the South China Sea.

The official, Vi Kien Thanh, did not say which scene Vietnam hadn’t liked. Several commentators wondered if he meant the one showing Barbie, played by Margot Robbie, standing in front of a crudely drawn world map. Some also noted that the nine-dash line in that scene appears to lie very far from Asia.

If that is, indeed, the offending map, “I really can’t see what the fuss is about,” said Bill Hayton, the author of books on Vietnam and the South China Sea.

“The map in the film appears to bear no relation to a real map of the world,” Mr. Hayton added. “This looks like Vietnam’s censors trying to demonstrate their patriotism and usefulness to the regime.”

Vietnam’s Foreign Ministry did not immediately respond to a request for comment. Neither did Warner Bros. The American movie studio told the Reuters news agency on Thursday that the “Barbie” map of the South China Sea was a “childlike” drawing with no intended significance.

Why is the South China Sea important to Vietnam?

Vietnam and China are neighbors with an extraordinarily complex relationship. On one hand, both are ruled by a Communist Party, making them ideological allies. They’re also busy trading partners that share an 800-mile border.

Yet China occupied Vietnam for a millennium and invaded it as recently as 1979. And under Xi Jinping, China’s powerful leader, Beijing has built military outposts on contested islands in the South China Sea. It also rejected an international tribunal’s landmark 2016 ruling that sided with the Philippines by saying that China’s expansive claim to sovereignty over the sea had no legal basis.

The South China Sea, in particular, is so sensitive that Vietnam and China came dangerously close to an actual conflict there in 2014, after a Chinese company parked an oil rig in disputed waters off the Vietnamese coast.

All of that contributes to a fear among many Vietnamese that China could someday start a war in the body of water, which Vietnam calls the “East Sea.” Those concerns have helped shape Vietnam’s recent efforts to counterbalance its relationship with China by building stronger ties with the United States and other countries.

This ‘Barbie’ ban seems to fit a pattern.

Vietnamese censors have banned or altered several other movies that showed disputed areas as being under Beijing’s control. The list includes “Crazy Rich Asians” (2018), “Abominable” (2019) and “Uncharted” (2022), among others.

Why are Blackpink and the Philippines involved?

The Philippines is considering banning “Barbie” before its scheduled release there on July 19, with authorities saying this week that the movie was under review. A Philippine senator, Francis N. Tolentino, said that screening it would denigrate Philippine sovereignty.

Separately, a Vietnamese official said this week that the country’s Culture Ministry was trying to verify whether a Beijing-based Blackpink concert promoter, iMe, supports the nine-dash line. The promoter also apologized for displaying a map of the nine-dash line on its website, the Vietnamese news media reported.

The promoter’s Chinese website was inaccessible on Friday. Its Korean branch, along with Blackpink’s production company, YG Entertainment, did not immediately respond to requests for comment.

As of Friday, Blackpink, a K-pop juggernaut, was still scheduled to perform two shows at the national stadium in Hanoi, Vietnam’s capital, in late July.

What’s the view in China and Vietnam?

The “Barbie” ban was widely discussed online in China this week, after the Foreign Ministry in Beijing criticized Vietnam on Tuesday for linking the South China Sea to “normal cultural exchange.” Many Chinese social media users have been dismissive of the spat, saying that Hollywood would always choose China over Vietnam.

By contrast, a few prominent Vietnamese observers said in interviews this week that their government’s “Barbie” ban was consistent with earlier efforts to protect Vietnamese sovereignty in the sea, and partly a reflection of the Communist Party’s sensitivity to domestic criticism of its China policy.

The “Barbie” ban was also successful, they added, because it got the international news media talking again about Vietnam’s territorial grievances.

Chau Doan contributed reporting from Hanoi, Vietnam. Li You contributed research from Shanghai.