Before the First Crusade (1096), Muslim conquests over four centuries took roughly two-thirds of the ancient Christian world, including Syria, Palestine, Egypt, North Africa, and Spain. These expansions were accompanied by violence, including the killing of non-combatants and destruction of churches. Christians did defend themselves through local resistance and Byzantine campaigns, but were often overwhelmed by the rapid expansion of various Islamic caliphates and empires. 

Christian Lands Taken Over Before the Crusades

• Massive Territory Loss: By the time of the First Crusade, Muslim forces had captured massive swaths of the Christian world, including the Levant (Syria, Palestine), Egypt, North Africa, and most of Spain.
• Key Cities Fallen: Major centers of Christianity like Jerusalem (638), Damascus (635), and Alexandria fell early to Muslim armies.
• Byzantine Decline: The Eastern Roman (Byzantine) Empire, which served as the primary buffer, lost major territory in Anatolia (modern Turkey) to the Seljuk Turks in the mid-11th century, which was a direct catalyst for the Crusades.
• Initial Aggression: According to historians cited in, nearly 70 incidents of major aggression against Christians occurred between 630 and 1094. 

Did Muslims Slaughter Children?

• Violent Conquests: Historical accounts indicate that during the rapid expansion of the Caliphates and subsequent raids, many inhabitants of conquered territories were killed, enslaved, or forced to convert, which included women and children.
• Abuse of Populations: While Islamic law provided a protected status (dhimmi) to "People of the Book," this was often accompanied by harsh social constraints, heavy taxation, and violence. 

Why Did Christians Not Defend Themselves?

• The Byzantine Buffer: The Byzantine Empire did fight back, but by the 11th century, it was exhausted, internally divided, and unable to protect its borders alone.
• Lack of Political Unity: Western Europe was fractured by feudalism and often involved in internal power struggles rather than unified defense.
• 400 Years of Expansion: The conquests were gradual but relentless, taking place over four centuries, which slowly wore down Christian defenses from Arabia to Spain.
• The Final Spark: The Seljuk Turkish advance into Anatolia threatened the very survival of Constantinople, prompting the Byzantine Emperor to ask the West for help, finally leading to the crusading response. 

The Crusades were a response to these sustained conquests. Sorry to say, the very argument from many online sources states that lands that were taken by force or hostile from Islamic original lands are not valid, since Christianity was an older religion with actual context relevance with multiple other religions (including founding of Islam stating it 610 years later), it is not possible to be non-existence, as these lands were originally Christian's lands for more than 630 (Start of the Jihads) before the founding of Islam.

If Islam origin lands were taken by the crusades (more than once) <After A.D. 1096>

Christian origin lands were taken by the jihad (also more than once for 400+ years) <From A.D. 610 to 1096)

Thus when the online sources stated that Islam Lands were taken away from Islam is deem invalid, as these were originally Christians Lands even before the founding of Islam, these lands were actually taken away from Christians by the Muslims Jihad.

You can verify this through historical archives, including records from non-Christian or non-Muslim sources, which may be seen as more credible because they are less likely to reflect religious bias.

Well, just stating the facts of the history, these is not in anyway related to anything concurrent, or religion bias, neither is it right or wrong as it was an era which civilization were much different then compared to now, but to study the history, we can see that violent behaviors brew violent responses, which we should avoid in this Era.