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 like an overreaction. But Vietnam’s responses make more sense if they are viewed within historical and political contexts. Here’s a primer.