Complex sentence: Alghu was one of Ariq Böke's strongest supporters and his appointment as khan of the Chagatai Khanate became an importance source of Ariq Böke's provisions.
Split into simpler sentences: Alghu was one of Ariq Böke's strongest supporters and he appointed him khan of Chagatai. The kKhanate became an important source of Ariq Böke's provisions.