Complex sentence: It speaks about the Islamic empire at its best and worst and aims to forewarn the Muslims of the sub-continent, make them more aware of their past and help them learn from their forefathers' mistakes.
Split into simpler sentences: It speaks about the Islamic empire at its best and worst. The aim of this writing was to forewarn the Muslims of the sub-continent and make them more aware of their past and help them learn from their forefathers' mistakes.