Her Royal Highness Seems to be Angry Series by Kou Yatsuhashi

In a remote kingdom, there lived a princess, adored by her subjects and wielding powerful magic. But as her land was ravaged by an endless war, she lost her people, her family, her loved ones, and eventually, her own life. Until she opened her eyes and awoke in a place she’d never seen before! A thousand years have passed, and she finds herself reincarnated into someone else's body... moreIn a remote kingdom, there lived a princess, adored by her subjects and wielding powerful magic. But as her land was ravaged by an endless war, she lost her people, her family, her loved ones, and eventually, her own life. Until she opened her eyes and awoke in a place she’d never seen before! A thousand years have passed, and she finds herself reincarnated into someone else's body. Realizing the person she's now living as is despised by her own family and even her fiancé, the former princess struggles to understand this new world and the events that have transpired since her death.  There’s a lot to be upset about, but first on the how in the world did future magic turn out so lame? less