Not all of Westeros was ready to wage war against the now-three-centuries-ensconced monarchy. Many lords and houses of note remained loyal to the Targaryens throughout, or abstained from the fighting as much as possible, and both Robert and Ned needed to return to their castles to rally and organize their armies. During these early stages of the war, Robert proved himself as both a warrior and a battle commander. He started by going east from the Eyrie to Gulltown, where he led his men over the city walls. He killed the leader of the defense, Lord Marq Grafton, and when the port city was secured, sailed south towards the Stormlands. With fresh men in tow, he won three battles in one day at Summerhall, the site of Aegon the Unlikely's demise. With each victory, the Baratheon army grew.

Robert suffered his first defeat at the Battle of Ashford, a disorganized affair in which Baratheon forces were set upon by Lord Randyll Tarly and a segment of the Tyrell army. Though casualties were minimal, Ashford's strategic location allowed Mace Tyrell to lay siege to Robert's brother Stannis at Storm's End, the ancestral home of the Baratheons. The siege would not be lifted until the end of the war, but a smuggler named Davos Seaworth brought badly needed supplies through the Tyrell barricade to sustain Lord Stannis's people.