Ranbodori was an warrior's act of looting things and robbing people after war from the Sengoku Period (Period of Warring States) through the Azuchi-Momoyama period. It was commonly called randori for short.
Many of the troops in those periods were farmers, who voluntarily participated for food supplies or for the purpose of looting on battle fields. The loot gained from robbing was put on the market, while daimyo (feudal lords) overlooked these violence and encouraged the acts in their neighborhood. They were not considered wrongdoing, but were generally accepted.
In the event of poor harvest, water damage, or epidemic, daimyo made war on neighboring territories for food. This led to acquisition of territories, which were then given to the daimyo's vassals to ease their ambition to come through the ranks.
They attacked villages around battle fields, where they took all of the farm crops and kidnapped women and children for money or for use as slaves.
Battle of Okehazama
According to a theory put forward by Hideo KURODA, professor emeritus at the University of Tokyo, Nobunaga ODA beat IMAGAWA 'because Oda conducted a surprise attack on the Imagawa army, who were caught off guard while in the act of looting private homes.'
In the Meiji period, it was particularly believed by the army that the Oda army attacked by way of a detour, but in recent years, the belief that they attacked head-on has been favored, based on Shincho Koki (Biography of Nobunaga ODA).
Focusing on Koyo Gunkan (record of the military exploits of the Takeda family), however, Kuroda determined that 'lapses of memory were seen, but the stories are not maliciously fabricated; this is a historical material of good quality based on their experiences.'
Given the fact that the Takeda clan and the Imagawa clan were allied, he said, 'it would be hard to believe that they mistook the reason for the Imagawa's defeat, and this is based on a reliable source obtained from the losers by a third party.'
Koyo Gunkan states that 'just when the Imagawa army thought they had won the battle (another previous battle) that day and went off for looting, the Oda army was mixed up in them and took Yoshimoto's head,' while another historical source confirms that Ieyasu TOKUGAWA was quoted as saying 'the Imagawa army was looting, and caught off guard.'
Calling looting "Randori," Kuroda named his new theory 'Sudden Attack in Randori-State Theory.'