The Great Tang's Strongest Imperial Son-in-Law

I woke up to find myself transmigrated into the Tang Dynasty. The unfortunate Second Young Master Du faces two choices from the start: follow the course of history, marry a princess, and get executed by Li Er a few years later; or refuse the imperial edict, decline to become Li Er’s son-in-law, and face the grave crime of disobeying an imperial decree. The fallen-from-favor Second Young Master Du refuses Li Er’s edict and is demoted to guarding the gates of Youzhou City. Youzhou falls, and its people suffer. At the critical moment, Du He arrives and turns the tide single-handedly, driving back the fifty-thousand-strong vanguard of the Turks. He fights covered in blood and makes his name in a single battle. He campaigns against the Turks and sweeps across the north; he crushes Goguryeo and wins the people of the Tang Dynasty a peaceful, stable place to live...