How did the Muslim community got divided into sects?

I am going to continue reading the book and writing daily review. In addition, I am also going to write a rebuttal (in bold font) when I feel the author has missed out crucial facts/discussions.
Part II of the book deals with the manner in which the Muslim community has been divided into 73 sects.
Al-Baghdadi started the chapter briefly mentioning that the first ever division was over the mortality of the Holy Prophet (may peace and blessings of Allah be upon him and his pure family). Some didn't believe that the Holy Prophet died/he could die. And he mentioned Abu Bakr giving an authoritative declaration that put this issue to rest.

• Here, the author did not mention name of people who doubted the death of the Holy Prophet. At least we know (according to some traditions) that one of the doubters was Umar al-Khattab (the second caliph).
• Some Sunnis have told me that this reaction (to doubt the death of your closest companions/friends/a member of your family) is normal. If so, then al-Baghdadi is making a really big issue out of it.

The next cause of the division (according to the author) was on where the Holy Prophet should be buried (burial site). The author stated that they came to an agreement by burying him at a place where he died.

• Interesting to note that the author did not mention names of prominent companions that were mostly missing from the Prophet's funeral (ceremony and the ritual). Some of them were bickering over who should be the next caliph. Please search for 'Saqifa of Banu Saida'.

The next division in the Muslim community was over Fadak. Fadak was an agricultural land owned by the Holy Prophet and given to his (Prophet) daughter, Fatima, while he (Prophet) was still alive. The giving of Fadak was a commandment from al-Mighty.

The following verse was reveled to the Holy Prophet (may peace and the blessings of Allah be upon him and his pure family)

وَآتِ ذَا الْقُرْبَىٰ حَقَّهُ وَالْمِسْكِينَ وَابْنَ السَّبِيلِ وَلَا تُبَذِّرْ تَبْذِيرًا {26}
[Shakir 17:26] And give to the near of kin his due and (to) the needy and the wayfarer, and do not squander wastefully.
[Pickthal 17:26] Give the kinsman his due, and the needy, and the wayfarer, and squander not (thy wealth) in wantonness.

• The author made an erroneous conclusion here. He said that the issue was settled when Abu Bakr presented a hadith to deny Prophet’s daughter the land that was already given to her while the Prophet was still alive.
• Yesterday, we went through a list of heresies (according to al-Baghdadi). Generally, heresies are controversial beliefs and we are urged to stay away from them. Two of the heresies mentioned by al-Baghdadi were i) Believing that the Islamic laws can/will be abrogated at the end of time and ii) allowing what is forbidden and disallowing what is lawful.
• Didn’t Abu Bakr just abrogate the law of inheritance in favor of something that he claimed he heard from the Holy Prophet?
• Shouldn’t he look for the answers in the Holy Quran (words of Allah swt) before exercising his personal Ejtehad?
• The Fadak issue was never resolved. The Prophet’s daughter refused to speak to either of the two men until to the day she died. She died very young. She also did not allow the two shaykhs (Abu Bakr and Umar) to attend her funeral.

I am ending my entry with a link to a sermon by Fatima az-Zahra about Fadak