Complex sentence: Seemanchal is a subregion of Mithila region in the northeastern part of Bihar consisting of four districts-Araria, Purnea, Kishanganj and Katihar which was backward region of India, but now it is in developing phase.
Split into simpler sentences: Seemanchal is a subregion of Mithila region in the northeastern part of Bihar consisting of four districts-Araria, Purnea, Kishanganj and Katihar. It was one of the backward areas of India, but now it is in developing phase.