The Land of Woods (林の国, Hayashi no Kuni) was once home to an Anbu group called the Prajñā Group.
History
In the anime, Konohagakure once sent a team to meet with the Prajñā Group in an attempt to establish an alliance, but anticipating a betrayal on their part. The Prajñā Group did betray them, and were all but exterminated.[1]
Years later, their remnants tried assassinating the Candidate Sixth Hokage — Danzō Shimura, who had been the one to send the team that killed many of their shinobi, but failed and were killed.[2][3]