Muslims believe that Islam is a critical and mandatory upgrade to the existing religions of Judaism and Christianity and in its early years, had believed that they were obliged to convert the world around them. This crusade took its most extreme form in a violent interpretation of the concept of “jihad” wherein Muslims would wage war against non-Muslims for the purpose of converting them.
Islam even went beyond religious conversion with the establishment of the sharia which is the codification of Islamic holy law and also imposes a way of life that touches every aspect o fit. Conquered peoples found their society drastically changed and those threatened have militarized heavily to avoid such fate. With such a extremely strong religious conviction, Muslims were able to spread Islam expand very rapidly and transforming the societies of countries and regions far beyond the borders. These conquered territories were then termed as dar al-Islam.
In spite of the spectacular expansion of Islam up to the 750 BC driven by religious fervor, it was still led by leaders who may differ in their views of Islam. The Abbasid dynasty right after that time chose to hold off the goal of conquest in favor of peaceful administration of dar al- Islam. Islam still continued to grow but was due more to proselytizing and voluntary conversion. This period have a glimpse of another Islam that can is still fiery but no longer violent bloody. This was perhaps fortunate for the world whose capability for greater destruction continually grows with military technology. The Abbasids concentrated instead in progressing civilization within it borders by strengthening laws, building wealth and promoting education. Society was regulated by religious officials (ulama) and judges (qadis). Up to this
day, this societal structure of strict religious laws is followed in many Muslim countries. Religious fervor by conquest was replaced by aggressive vigilance of non-Muslim influences from outsiders. Extreme reaction can still lead to violent jihad as espoused by Islamist terrorist organizations.