Between the 630s and the 740s Arab-Muslim armies destroyed the Sasanian empire and stripped Byzantium of its southern provinces, creating a single polity from the Atlantic to Central Asia. The characteristic instrument of rule was not expulsion but the dhimma: Christians, Jews, Zoroastrians and later others retained their communities, law and worship in exchange for tribute, principally the jizya poll tax, together with legal subordination that hardened into formal disabilities from the eighth century onward. Conquering forces were settled in purpose-built garrison towns rather than dispersed among the conquered, which limited displacement but created a durable structure of separate and unequal populations. Later Islamic tradition also records the removal of Christians and Jews from the Hijaz under Umar I. The demographic effect was gradual: conversion and Arabisation took centuries, and Egypt and Syria retained Christian majorities long after the conquest. The entry records a change of sovereignty and a legal regime of subordination, not a mass deportation.
Rashidun and Umayyad armies conquered Sasanian Iran, the Byzantine Levant, Egypt and North Africa, founded garrison towns for Arab settlers, and placed conquered non-Muslims under a tributary 'dhimma' regime
There is no census for the seventh century. McEvedy and Jones's regional estimates give roughly 12 million for Iran and Iraq, 3-4 million for Syria and Palestine, 4 million for Egypt and 3-4 million for North Africa around 600-650 CE, giving an order of magnitude of 25-30 million. Later Islamic tax registers (the jizya rolls) count dhimmi households in particular provinces but cannot be aggregated backwards. Conversion was slow: Bulliet's curve from onomastic evidence suggests majorities of Muslims were reached only in the ninth to tenth centuries.
No defensible figures. The conquests involved pitched battles, sieges and the sack of some cities, but no source or modern reconstruction supports an aggregate death toll, and much of the territory changed hands by capitulation treaty rather than storm.
Syria, Saudi Arabia, Iraq, Egypt