No, Caliphs are not allowed to change the orders of allah nor the prophet.
However, the prophet (PBUH) specifically asked us to follow the 4 rightly guided caliphs(Abu baker, Umar, Othman, Ali) because they are the best people Islam has seen. The hadeeth found in At-tridmhi and Abu Dawud
The Messenger of Allah (PBUH) gave us a sermon by which our hearts ...
The justification was that they were following the commands of the Quran, among them:
يا أيها الذين آمنوا قاتلوا الذين يلونكم من الكفار
O you who have believed, fight those adjacent to you of the disbelievers
— Quran 9:123
As the Persians and Romans were those adjacent to the Muslims during the caliphates of Abu Bakr and Umar.
فيه أنه ...
Umar ibn Al-Khattab, the second Caliph, married Atiqa bint Zayd.
وفيها تزوج عمر بن الخطاب عاتكة بنت زيد بن عمرو بن نفيل، وهي ابنة عمه
Umar ibn Al-Khattab married Atiqa bint Zayd bin Amr bin Nufayl, who was the daughter of his uncle
— The Beginning and the End by Ibn Kathir, events of 12th year of Migration
This took a lot of research and reading about the incidents you mentioned, but it is very difficult to know exactly which part of an event you are referring to with only the information you have provided. I could not find any of the events you are referring to in the manner you mentioned in books that are accepted by Muslims as references.
I will give an ...
The Kalifah is chosen by Ahlul Ikhtiar, and the requirements of the Kalifah are the following:
Must be Muslim
Must be Mature
Must be Sane
Must be a freeman and not a slave
Must be knowledgeable
Must be Righteous
Must be a Male/Man
Have prudence in opinion/ Wisdom
Must have firm qualities, like bravery and fairness
Must have a healthy body and ...
This is not going to be an easy task as not too many companions married their cousins. One companion that I know of is 'Abdullah ibn 'Umar ibn al-Khattab who was married to his maternal cousin, Zainab bint 'Uthman ibn Madh'ūn.
His mother was Zaynab bint Madh'ūn. Her brother, 'Uthman ibn Madh'ūn had a daughter named Zainab from his wife, Khawlah bint Hakim ...
I think what people wrongly think about ancient times (and by extension the times of the Islamic Conquests) is that peace was always assumed. Nowadays, we have the UN and a lot of International Conventions that make it so that war has to be declared, but in previous times, war was not declared, peace was declared.
So, if there are two empires and there is ...
As Mujahid (مجاهد) has pointed out, there are various lists of qualifications in old sources. All the Sunni law schools agree that the Imam/khalifa must be from the family of the Prophet (ahl al-bayt), in the sense that he must at the very least be from the Quraysh. This invalidates the spurious claim of the Ottomon sultans to be caliphs (to say nothing of ...