Whiterun Hold has been neutral territory during the Skyrim Civil War, with skirmishes on both sides taking place in the Hold and Fort Greymoor switching hands between the Empire and Stormcloaks on a regular basis. Jarl Balgruuf refused the Legion's right to garrison troops in Whiterun city, on the other hand he also refused to acknowledge Ulfric's claim. After an unknown period of time, Ulfric started planning an attack on Whiterun. Shortly after Balgruuf got to know of this news, he declared his allegiance to the Empire.
Jarl Ulfric Stormcloak sent his axe to Whiterun, which Balgruuf returned, meaning he did not back the Stormcloaks. Since Ulfric Stormcloak saw those who weren't with him as against him, Balgruuf instantly ordered his steward to write a message to General Tullius, requesting Legionnaires.
Jarl Balgruuf, after getting a message from General Tullius in which some of Ulfric's plans were recorded, decided to send Ulfric his axe. Ulfric decided to send the axe back, which meant they would go to war, which is the response that Balgruuf suspected.
The Legionnaires sent by General Tullius arrived just in time to fight against the Stormcloaks and catapults are stationed in the city to ward off the invasion. The Stormcloaks however, have also brought catapults with them and intend to rain large fireballs on the city. Although the siege will keep the frail city walls intact, the soldiers will be forced to fight in the flames. The Imperial Legion has set up water brigades to mitigate the danger of fighting in an inferno and prevent the fires from getting out of control. The Imperials had blocked the first passage going into the wind district, and had set up various barricades in the city. Victory in the battle depends on if the Imperials can prevent the Stormcloaks from dropping the drawbridge, which is integral for keeping Whiterun from being overrun. 
- ↑ If the Imperial Legion wins the battle, Whiterun remains part of the Empire, however, if the Stormcloaks win, Vignar Gray-Mane gets appointed as Jarl.
- ↑ Imperial Generals and Imperial Field Legates only appear if the Stormcloaks are sided with, likewise, Legate Rikke only appears if the Empire is sided with.
- ↑ Stormcloak Generals and Stormcloak Field Commanders only appear if the Empire is sided with, likewise, Galmar Stone-Fist only appears if the Stormcloaks are sided with.
For the battle in The Elder Scrolls V: Skyrim
- ↑ 1.0 1.1 1.2 Dialogue with Balgruuf the Greater
- ↑ Dialogue with Captain Aldis
- ↑ Dialogue with Agnis
- ↑ 4.0 4.1 Dialogue between Legate Rikke and General Tullius
- ↑ Dialogue of the Last Dragonborn during Message to Whiterun (Imperial)
- ↑ 6.0 6.1 Dialogue between Balgruuf the Greater, Proventus Avenicci and Irileth
- ↑ Dialogue with Balgruuf the Greater
- ↑ Events of Message to Whiterun
- ↑ 9.0 9.1 Dialogue with Ulfric Stormcloak
- ↑ Dialogue between Balgruuf the Greater and Proventus Avenicci
- ↑ Dialogue between an Imperial Legion Soldier and Legate Quentin Cipius
- ↑ 12.0 12.1 Events of Battle for Whiterun (Imperial) and Battle for Whiterun (Stormcloaks)