In 2017, Chinese tech startup ByteDance Ltd. purchased Musical.ly, a Chinese lip-sync video app with 200 million global users that was especially popular with American teenagers. The following year, ByteDance folded Musical.ly into its own short video app, TikTok. The new TikTok app held onto the Musical.ly user base, giving it a significant foothold in the U.S. market. Since then, users worldwide have downloaded TikTok more than 2 billion times. It’s a bona fide cultural phenomenon in the U.S., where it has 50 million daily active users and teenage influencers earn huge followings and six-figure salaries. TikTok’s global success is matched by its globe-spanning controversies: it’s fielded and denied charges that it censors content, violates user data privacy, and shares data with the Chinese government. India banned TikTok over those concerns; the Trump administration has threatened to do the same unless an American company buys the app's U.S. business by Nov. 12. The outcome of that ultimatum is uncertain after Beijing announced in late August that it can approve or block the sale of artificial intelligence technology, including TikTok’s crucial algorithm, meaning the Chinese government will have a say in any TikTok deal.