Great Tang: I, the Crown Prince, Conquered the Turks from the Start

An accident transmigrated me to the prosperous Tang dynasty, where I became the crown prince of the Eastern Palace. The dynasty is strong in arms and soldiers, but the borders are constantly under attack, and foreign tribes watch us like hawks. With Li Er troubled by these challenges, this is the perfect time to show what I can do. Why would I, Li Chengqian, need to stage a rebellion to take the throne?