Every listed company in the US needs to disclose its subsidiaries to potential investors. These are found in form EX-21 or EX-21.1. To View subsidiary forms across multiple years simply visit
a company's ShareSEER page
and view the subsidiary section on the right side of the result page.
Any major acquisitions eventually find their way in the subsidiary section. I have a feature on my list that would allow users to see Subsidiaries that were added or removed year over year. If you think this would be useful shoot me a note at firstname.lastname@example.org
If you liked this read more at the shareseer blog.