Commonly, it is said that Mahabharata war happened for the sake of honour of Draupadi. Pandavas wanted to take revenge from Kauravas for insulting her and Lord Krishna helped them. But then we see that Pandavas sent a peace mission to Kauravas. He said to Kauravas that if they would give Pandavas even 5 villages, then the war can be averted. Here it seems like Pandavas only cared about their kingdom. Then what about the vow of Bhima to kill all Kauravas ? Was Mahabharata really a war of Dharma or if it was just a civil war between the princes for sake of throne why did Lord Krishna got involved in it?
The Pandavas definetly wanted Duryodhana to have some payback.
Remember Draupadi who was ill-treated, while in her season, in the midst of the assembly! Remember the deprivation of the king through dice by thyself and Subala's son! Remember that great woe suffered by us, in consequence of thee, in the forest, as also in Virata's city as if we had once more entered the womb! I shall avenge myself of them all today! By good luck, O thou of wicked soul, I see thee today! It is for thy sake that that foremost of car-warriors, the son of Ganga, of great prowess, struck down by Yajnasena's son, sleepeth on a bed of arrows! Drona also hath been slain, and Karna, and Shalya of great prowess! Subala's son Shakuni, too, that root of these hostilities, hath been slain! The wretched Pratikamin, who had seized Draupadi's tresses, hath been slain!
Even Yudhishthira mentioned Duryodhana about insulting Draupadi.
Thou hadst at one time especially endeavoured to burn us to death and to take our lives by means of snakes and other kinds of poison and by drowning us! We were also wronged by thee, O king, by the deprivation of our kingdom, by the cruel words spoken by thee, and by thy maltreatment of Draupadi! For these reasons, O wretch, thy life must be taken! Rise, rise, and fight us! That will benefit thee!"'
Both. Yudhisthira had no lust for the Kingdom. Bhima was the one who was driving him. Well, Yudhisthira said that if they don't return the kingdom which was the deal then then the war will happen. The point is clear that Yudhistara didn't forgive the Dhritarashtra's son but he never wanted to the war as it would cause the death of many innocents. Thats why Krishna was sent for peace. Even if the war had not taken place, the death of Dhritarashtra's sons by Pandavs was inevitable. It's just that their ignorance killed many innocents like Abhimanyu, Ghatotkacha, etc.
It is clearly written that the war was an act to give the world greatest knowledge i.e. Shri Bhagwat Gita
"He said to Kauravas that if they would give Pandavas even 5 villages, then the war can be averted": This is to show how Arjuna wanted to avoid the war and not kill his relative brothers. Hence he is ready to accept 5 villages to avoid war which is cowardness according to this dharma i.e. kashtriya
Krishna then convinced Arjuna to get into a war to kill all the Adharmi people and it is said that killing then won't add sin.(Not applicable now in this world though)
Hence Mahabharata was a way to give Shri Gita to the people. And to kill all the negativity from the world and enter Sanatan world