The Japanese campaign in the Shan States was a shrewd tactical maneuver in the battle for Burma. It hastened the fall of Burma by weeks, if not months, and increased greatly the amount of materiel captured by the invaders or which had to be destroyed by the British and Chinese. The righting began in that area in mid-March with patrol action on the Thailand border of Karenni, a small British protectorate adjoining the Shan States on the south; but it was not until April, following the fall of Toungoo, Burma, that serious fighting occurred. Previously the only approach the Japanese had to this mountainous district was by boat up the swift, treacherous Salween river, or over jungle trails from Thailand. But with the capture of Toungoo at the end of March, they had a road from Burma to Karenni and on to the Shan States.