Under the leadership of A. Z. Phizo, the Naga National Council unsuccessfully led a secessionist movement. When the Constitution of India was first released in 1950, the Naga Hills District was placed in Part A category of tribal districts as per the Sixth Schedule. The Part A areas were supposed to be governed by the Government of Assam in collaboration with the Autonomous District Councils. However, the Naga leaders refused this scheme. Subsequently, the Naga Hills District, along with the Tuensang Division (then a Part B area in the North-East Frontier Agency) were made a new administrative unit under the Ministry of External Affairs in 1957. After negotiation with the secessionists, this administrative unit was later made a full-fledged state called Nagaland.