Revelation in the holy Quran and in their strong faith
Revelation in the holy Quran and in their strong faith
The Muslims didn't conquer lands peacefully, they had armies and fought like any other conqueror. Many of the lands they conquered were weak from years of war, most historians agree that the Sassanid Persian and Byzantine Roman empires were militarily and economically exhausted from decades of fighting one another.,
The Byzantine and Persian empires were weak.
The rest of the world outside the Persian and Macedonian empires.
The first probes into Byzantine (eastern Roman) territory began immediately after the conclusion of the last war between the Byzantine and Sassanid Persian Empires. One of the earliest battles of note was the battle of Mut'a in 629 and the most significant afterwards was the battle of Yarmuck, between 635-636 AD when Byzantine forces were badly defeated.
The question as phrased is nonsensical. The Byzantines were Orthodox Christians, not Muslims. In fact the Muslims (under various empires) were almost consistently the enemy of the Byzantine Empire for nearly 700 years.
The Byzantine Empire was a powerful nation which controlled the trading hub of Constantinople, and whose government offered a greater degree of stability than most European nations at the time. The Islamic Caliphate was a dynamic and prosperous nation which benefited from the zeal of its people and the power of its religion. Both empires were culturally and scientifically advanced.
Abu Bakr carried out the first conquests Rashidun Caliphate which was then expanded by his successor. He did not actually conquer any empires. He conquered mesopotamia (iraq) from the Persian (Sasanian) Empire, but not persia itself. He conquered Syria from the Byzantine Empire, but not the rest of this empire.
The Byzantine Empire, as well as the Persian Empire were located near the Arabian Peninsula, in the budding years of Islam.
Since the Byzantines and Sassanian Persians considered each other the only real civilizations in the region, they fought each other numerous times in the early 600s C.E. over control of what is today East Turkey and Iraq. These were intense religious wars (Christian vs. Zoroastrian) and greatly weakened both empires at just the wrong time, leading to a very porous southern defense and miscalculation of the Islamic Armies. Because of this, the Muslims were able to completely destroy Sassanid Persia and conquer over two-thirds of the Byzantine Empire.
Eqyptian Assyrian Babylonian Medo-Persian Greek Roman Byzantine and Ottoman Portuguese and Spanish Dutch and French British American/post colonial era
The spanish conquered the Inca and Aztec empires in America.