how is he associated with the mexican–american war?
He took part in it as a soldier of the American army.
Ulysses S. Grant
Grant served as regimental quartermaster, but yearned for a combat role; when finally allowed, he led a charge at the Battle of Resaca de la Palma. He demonstrated his equestrian ability at the Battle of Monterrey by volunteering to carry a dispatch past snipers, where he hung off the side of his horse, keeping the animal between him and the enemy.
who's the 18th president of the united states Ulysses S. Grant.
wiki:19682605
Ulysses S. Grant [SEP] Mexican–American War
Grant served as regimental quartermaster, but yearned for a combat role; when finally allowed, he led a charge at the Battle of Resaca de la Palma. He demonstrated his equestrian ability at the Battle of Monterrey by volunteering to carry a dispatch past snipers, where he hung off the side of his horse, keeping the animal between him and the enemy. Before leaving the city he assured some wounded Americans, he would send for help. Polk, wary of Taylor's growing popularity, divided his forces, sending some troops (including Grant's unit) to form a new army under Major General Winfield Scott.