What are the contributions of the four guided caliphs in the spread of Islam?

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

The contributions of the Rightly-Guided Caliphs in spreading Islam and supporting it are so great that it is difficult to list and enumerate them in a brief Fatwa. In summary, all the goodness in which Muslims are, such as knowledge and guidance, the Rightly-Guided Caliphs have a merit and favor over the Ummah in it through their Jihad and their preaching of the religion. Ibn Taymiyyah said in his book Minhaj as-Sunnah: “As for the Caliphs and the Companions: All the goodness in which the Muslims are until the Day of Resurrection such as faith and Islam, the Quran and [Islamic] knowledge, sciences, and acts of worship, entry to Paradise, deliverance from Hellfire, their victory over the non-Muslims, and making the Word of Allah the highest, then it is only with the blessing of what the Companions did, who conveyed the religion and strived in the sake of Allah. Every believer who has believed in Allah, the Companions – – have merit and favor over him until the Day of Resurrection.

Allah knows best.