As-Salamu `Alaykum Wa Rahmatullahi Wa Barakatuh brother,
In the Glorious Qur'an, Almighty Allah states, "There shall be no compulsion in [acceptance of] the religion." [2:256]
When anybody does something he likes, he does so happily and is relaxed doing so, whereas if somebody is forced to do something, he does so because he is subdued and feels rather irritated doing so. In this verse, Allah, the Most Glorified and Exalted, indirectly states that none should be forced to do anything regarding religion, but should do so out of faith and free-will. In addition, Almighty Allah mentions in Surah Al-Kahf, "And say, "The truth is from your Lord, so whoever wills - let him believe; and whoever wills - let him disbelieve." [18:29]
Brother, the Rightly Guided Caliphs did not go against the teachings of Islam, and you could distinguish that from their name. In addition, 'Irbad bin Sariyah (may Allah be pleased with him) reported: One day Messenger of Allah (may Allah bess him and grant him peace) delivered us a very eloquent sermon on account of which eyes shed tears and hearts were full of tears. A man said, "O Prophet of Allah, this is as if it were a parting advice. So advise us". He (may Allah bless him and grant him peace) said, "I admonish you to fear Allah, to listen and obey even if an Abyssinian slave is appointed as your leader. Because whosoever among you shall live after me, will see much discord. So hold fast to my Sunnah and the examples of the Rightly Guided Caliphs who will come after me. Adhere to them and hold to it fast. Beware of new things (in religion) because every innovation is a misguidance". [Abu Dawud and At- Tirmidhi]
The aim of conquest is not to make people convert to Islam against their will, but to open the country for Muslims, as it is even called 'al-Fatūḥāt al-Islāmiyya'. At those times, expanding land was very important. In addition, Muslims are not allowed to kill any innocent people, and you could tell that too as Almighty Allah stated, "O you who have believed, prescribed for you is legal retribution for those murdered - the free for the free, the slave for the slave, and the female for the female. But whoever overlooks from his brother anything, then there should be a suitable follow-up and payment to him with good conduct. This is an alleviation from your Lord and a mercy. But whoever transgresses after that will have a painful punishment." [2:178]
In addition, Almighty Allah said, "And do not kill the soul which Allah has forbidden, except by right. And whoever is killed unjustly - We have given his heir authority, but let him not exceed limits in [the matter of] taking life. Indeed, he has been supported [by the law]." [17:33]
The Caliphs (may Almighty Allah be pleaed with them) also warned their troops of killing innocent people when going to conquest.
That's why everybody loved the Muslims even after they had carried out many conquests. May Allah forgive me if I made any mistakes in this post... Best regards.
As-Salamu Alaykum.
