The sea people are a group that appear in accounts about the ancient Middle East but always in very vague terms. I believe they contributed to the downfall of several middle eastern states, Ancient Egypt in particular. I’ve done some cursory research on the topic and found almost nothing on them. I know there was a book written on them recently (1188: the year civilization collapsed), but I’m wondering if there’s been new findings, first hand accounts or archeological sources?
Not to forestall further (in-depth comprehensive) answers, but there's a section of our Frequently Asked Questions page about the Sea People featuring not only a great explanation of where the term 'Sea Peoples' comes from, and why it isn't that mysterious by /u/bentresh and a good summary of what we know about the phenomenon by /u/kookingpot, but also an AMA with the author of 1177 BC: The Year Civilization Collapsed.