A Princesa Real Ja Myung Go (2009)

both are historical romances with a romeo and juliet theme.

both have a Romeo and Juliet theme but will leave you a smile on your face. another good sageuk drama. :)

Both shows have main characters with realistically muddled/mixed intentions.
Female lead has faced a tragic past, yet is willfull/self reliant and wise, while the male lead is often rash and childish but also honest, gentle and caring -- this relationship ( in both shows ) is built upon a strong friendship and mutual respect before evolving into romantic love.

lots of tragic ill fated lurv n all that too. love triangles in both shows involving relatives (in ja myung go sisters in love with the same man, in imperial doctress brothers in love with the same women)

court machinations n manipulations abound...

both shows are melodramatic but entertaining and plotwisty in the juiciest (though admittedly sometimes most absurd) way

If you're looking for romance tragedy...
-ML in both dramas took advantage of their FL, then take over the others' tribe/country and killed her loved ones and people.
-They also uses other women to further their ambition.
-Yep, both MLs are possessive jerks.
-Both FLs because of duty and responsibility to save their people, refuses to be with ML and rather sacrifice themselves.

Both are historical dramas
Both are about a lost/abandoned princess
Both are tragic stories
Both Female Leads are princesses that suffer while trying to find their identity

Both are historical dramas
Both have FL and ML that surprise you with their actions
If you liked one you will probably enjoy the other

Similar female leads - both are initially unaware of their royal lineage and work as spys/soldiers. Pre-Joseon era. Complicated love stories and political intrigue. Sisters fighting.