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"Mother Earth Mother Board" (1996) by Neal Stephenson is great narrative nonfiction on the subject: https://www.wired.com/1996/12/ffglass/

This is a pretty fun starting point: https://www.submarinecablemap.com/

NANOG has presentations on low-level stuff. A comment of mine from a few days ago links to some videos:

I'm sure you'll get a bunch of "related" videos on YouTube after watch them.