On Sunday, millions of phones across the United States buzzed with a peculiar notification: “TikTok is here to stay!”

The alert led to a video post by TikTok’s interim global head, Vanessa Pappas. Without directly mentioning the Trump administration’s proposed ban, which was expected to go into effect that day, she thanked users for their support. Without naming Oracle or Walmart, she said the company was “thrilled to share” that it was working with “a U.S. tech partner” to continue operating with “no change to our users here in the U.S.”

The video’s careful omissions called to mind a hostage film; still, many of the more than 200,000 comments on the post were grateful for any proof of life. “IM NOT JOBLESS,” wrote one user, itsnotjakefuller, who has more than 1 million followers on the platform. “Bruh, I? quit my job two weeks ago. This is good news,” wrote dadlifejason, who just passed 3 million. The response from the user fatraco0n was among the most popular: “You make me feel safe Vanessa.”

For people who spend a lot of time on TikTok, the last few months have been surreal: a president with no presence on the platform has been agitating to ban it on the basis of national security. (TikTok is owned by ByteDance, a Chinese company.)

In contrast to mounting political criticisms of, say, Facebook and Twitter, platforms where the president is extremely active and invested, the government’s public case against TikTok has been largely speculative, citing theoretical dangers and hardly trying to appeal to the app’s users directly. It’s no surprise that the vague message from Ms. Pappas gave some users comfort, given how little this process has addressed them.

TikTok’s users are experiencing for the first time something long familiar to much of the world outside the United States: a flourishing online social space existentially threatened by diplomatic and political fights between states and corporations, with little input from those affected by their decisions. Likewise for WeChat, the Chinese messaging app used by millions in the U.S. to keep in touch with friends, families and colleagues abroad, which was set to be banned on Sunday until a federal court intervened.

To the limited extent that the plights of TikTok and WeChat have familiar precedents, they’re mostly overseas: China’s broad bans on foreign platforms including Facebook and Google; Russia’s “data localization” laws, which require foreign firms to store certain types of data locally; the occasional national shutdowns of Twitter, Facebook or YouTube during periods of political unrest in many countries around the world, including Egypt, Vietnam, Bangladesh, Sri Lanka, Turkey and others; or the Indian ban on TikTok and other Chinese internet services earlier this year.

“It is not surprising that American institutions rarely thought about what might happen to popular discourse if entertainment or information emanating from other shores is supplied on platforms and servers which might be based outside the country, with potential for data harvesting and exploitation for surveillance, spying or commercial gains,” said Daya K. Thussu, a professor at Hong Kong Baptist University and a co-author of “China’s Media Go Global.”

Worrying about a foreign government’s influence or access to data — or about whether imported competitors might hurt domestic firms — has been a burden for practically every country in the world except the United States, where many of the global internet’s most popular services were started. For a large majority of their users, Facebook, Twitter and Google are foreign firms.

TikTok users skew young, but older people following the company’s story on other social media, or in the press, have been similarly bewildered. Can the President just ban a social media app? How?

By September, such questions were superseded by events. There was an announcement by the Department of Commerce outlining its plan to disable the apps and remove them from app stores by Sept. 20. This was followed by a confusing, Trump-endorsed deal in which Walmart would take a stake in the company alongside Oracle, the enterprise software company, which claimed in a subsequent news release that TikTok “picked” the company as a partner because of its “faster, more reliable, and more secure” cloud.

Through TikTok, many social media users in America are getting a taste of what it’s like to socialize, work and live in an imported environment.

It’s an experience defined less by the platform’s features or particular traits — which, in this case, represent an evolution of, rather than a departure from, market-style American social media — than by the precarious conditions of its existence. It’s a personalized, intimate and largely domestic social environment that is also subject to the harsh and undemocratic forms of regulation that tend to arise when borders are involved. And its continued existence is contingent on a patchwork of cross-border threats, forcefully extracted concessions and political gamesmanship.

“The U.S. has dominated the digital platform market over the past two decades,” said Dal Yong Jin, the director of the Centre for Policy Research on Science and Technology at Simon Fraser University in British Columbia. It’s clear, he said, that the government sees the growth of Chinese platforms “as a threat to America’s global dominance.”

Geopolitically speaking, this is neither novel nor particularly shocking, according to Mr. Jin. “It is not unusual to witness this form of government intervention,” he said. “In fact, the current TikTok and WeChat affairs are not unusual in other countries.”

“I am certain that this kind of digital platform war will continue,” he added. “This is only the starting point.”

A decade ago, such platform wars were being waged abroad by American companies eager to expand. It was a period of corporate and mainstream political optimism, during which setbacks to expansion were treated as brief delays in an inevitable process — the next stage of American-led globalization, driven by Google, Facebook and Twitter.

Mark Zuckerberg, humbled by years of trying and failing to establish a foothold in China, has since changed his tune, testifying in front of Congress this year that his company is “proudly American” and warning that “China is building its own version of the internet focused on very different ideas, and they are exporting their vision to other countries.” In August, Instagram, which is owned by Facebook, introduced a feature called Reels, which bears a striking resemblance to TikTok.

In the last 10 years, social media users in the United States — of almost every political persuasion — have adjusted to the idea that, despite being full of friends, family, colleagues and peers, social platforms might not have their users’ interests at heart. They’ve heard stories of social platforms being used to drive countries apart, suppress particular views, enable campaigns of violence and undermine democratic processes.

They’ve been confronted with the possibility that a social platform doesn’t necessarily serve the voiceless and can in fact be beholden to those who are in power and used against those who are not. More directly, they’ve become accustomed to living their online lives in spaces ruled by aloof, distant figures whose motivations and loyalties are a subject of dark speculation. These aren’t lessons they learned from foreign firms, however, or even from how American firms operate overseas. These are lessons they learned at home.