You may know Shri Krishna had preached the Bhagavad Gita to Arjun in which the incidents of Mahabharata took place. It was the war held between Kauravas and Pandavas. This was the fiercest war that had never fought before and there is not the possibility to happen it in the future.
The search of the land for war began soon when the Mahabharata was decided. The land of Kurukshetra was decided by Shri Krishna. He wanted to eradicate the evils on the earth through this war and wanted to establish religion. He choose it because Kurukshetra is the land of Dharma.
Krishna also sent his massengers in all directions to know what they saw. One of the massenger witnessed an unusual incident in Kurukshetra. He said that he watched two brothers working in a farm. Due to heavy rain the elder brother asked the younger one to stop the rainwater flowing which was entering the farm. The younger brother refused to do so. Prompted by this refusal, in fit of anger the elder brother killed the younger one with the knife and used his corps to block the flowing rain water. Moreover, the messenger said that the elder brother had no guilt on his face whatsoever.
Hearing this, Krishna decided that this land is suitable for the war. And even the brotherly affection cannot ameliorate the animosity on such a land.