In the Mahabharata, Kurukshetra is where the great battle between the Pandavas and Kauravas was fought. It has been set down in the texts and in popular imagination as the place where dharma triumphed over everything else, restoring order to the universe.
The point is that war is and was abhorrent to most of the people even at the time the epic was being told and written. It was being denounced even more under the influence of pacifist religions such as Buddhism. Still the battle of Kurukshetra, in its most gruesome and violent outcome, was justified because it put an end to the forces opposing the rise of the good forces as embodied by the Pandavas.
The Pandavas are the heroes of the epic and, with Krishna by their side, their fight is the fight against evil. And thus Kurukshetra is established in the Hindu mind as dharmaksetra.
Apart from the Mahabharata, several other ancient texts too furthered the perception that this is god‚have chosen land on earth. According to Vamana Purana, this is where all creation emerged from. Also Kurukshetra is where King Kuru tilled the land. He sacrificed his body so that truthfulness, charity, justice etc would flourish in the world. Kurukshetra is called the gate of heaven in the Mahabharata and the battlefield as devabhumi is a belief that is firmly entrenched in the collective imagination.