Historically Correct Somewhat, Yet Poor Ending...Spoilers!

Historically, Jang Bogo does indeed get assassinated by Yum Moon (Yum Jang) with a concealed knife on the orders of Kim Yang. Later Jang Bogo's Cheonghae base is disbanded and most of his soldiers are scattered but this takes place over a period of time (not overnight).

But they could have still gone for a bit of a better ending by not having all the bad guys kill off all the good guys and get away with it all.

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wat are you lookin' at...