Could Islam really be a perfect religion?

[There is only one God]

I've been reading a book on pagan mythology and modern day religions. Not a single book said anything about Islam borrowing pagan beliefs. However, most of the books criticize one aspect of Islam which makes it far from being a perfect religion: The fact that Muhammad (PBUH) did not announce his successor, which caused 'the bloodiest of battles in history'. The book goes on to say that there are no perfect religions, as Islam's golden ages were over when the Shi'a and Sunni started warring each other back to the dark ages. Other factors of the decline of the Islamic golden age were:
1) Crusades
2) Mongol conquests

[Tanveer]

Dont you think people might have  started thinking too highly of the person the Prophet PBUH chose as his successor? And the civil war is politics, nothing to do with religion. Shias began as a political party then they decided to break off and create a totally different sect.