LONDON (AP) — Families stranded, honeymoons and vacations canceled, thousands of workers laid off: The sudden collapse of British tour company Thomas Cook and its network of airlines and hotels sowed chaos for hundreds of thousands of travelers and businesses around the world Monday.

Brought down by a variety of factors, including crushing debts and online competition, the 178-year-old travel agency that helped pioneer the package tour ceased operating in the middle of the night. Its four airlines stopped carrying customers, and its 21,000 employees in 16 countries lost their jobs.

The company...