Was the Prophet’s (peace and blessings of Allah be upon him) call to Islam by correspondence limited to kings and rulers outside the Arabian Peninsula, and how many times did he invite them to this?

The Messenger of Allah, peace and blessings be upon him, included the call to Allah Almighty in all his letters to kings outside the Arabian Peninsula. He corresponded with the Negus, King of Abyssinia (two letters), Heraclius and Caesar of the Romans (at least four letters), Al-Muqawqis, King of Egypt (one letter), and Chosroes (at least two letters), in addition to the Persian and Roman governors over some regions and Arab tribes in the Arabian Peninsula. He also campaigned against some of them, such as the Battle of Tabuk to confront the Romans and the Battle of Mu'tah in Al-Sham. Muhammad Hamidullah compiled the letters and treaties of the Messenger of Allah, peace and blessings be upon him, in his book: "Collection of Political Documents of the Prophetic Era and the Rightly Guided Caliphate."