Complex sentence: The Muslims had launched the movement under the banner of the All India Muslim League and Delhi was its main centre where the headquarters of All India Muslim League (the founding party of Pakistan) based since its creation in 1906 and remained there up to August 1947.
Split into simpler sentences: The Muslims had launched the movement under the banner of the All India Muslim League and Delhi was its main centre. The headquarters of All India Muslim League (the founding party of Pakistan) was based here since its creation in 1906 and up to August 1947.