Ikenie Daini Koujo no Konwaku: Hitojichi no Himegimi, Tekikoku de Chi no Saien to shite Daikangei wo Ukeru 

As the middle of three imperial princesses of the Fatenam Empire, Claire has always been seen as royal dead weight. So when Vallatenear emerges victorious in war, she's quickly offered up as a bride as part of the peace terms. Prepared for harsh conditions, torture, and even death, Claire is flabbergasted when she receives a warm welcome, and news that she's been betrothed to none other than the crown prince! It turns out her extraordinary intelligence is exactly what the kingdom has been longing for...a "Living Fount of Knowledge!"

(Source: MangaPlaza)