The assertion that Islam spread mainly because non-Muslims faced financial pressure to convert is false. The Islamic Empire practiced tolerance towards other monotheistic religions and conversions to Islam often occurred out of genuine belief or practical benefits, not merely due to the cost of taxes.
The statement that Islam gained more followers because it was expensive to not be a Muslim within the Islamic Empire is False. Although the Islamic Empire, specifically during the era of the Abbasid Caliphate, became wealthy, the spread of Islam was not primarily through economic pressure to convert due to high taxes for non-Muslims. In fact, the non-Muslim populations, known as dhimmi, paid a tax called the jizya, which was monetarily beneficial for the caliphate to maintain, hence discouraging forcible conversions.
The region under the Islamic Empire saw an era of tolerance in which prior monotheistic religions such as Christianity, Judaism, and Zoroastrianism were allowed to continue. Conversion to Islam happened over centuries, and many were drawn to Islam out of genuine belief or pragmatism. Additionally, there were instances where Muslim leaders would decline conversions to preserve their tax base.
The implication that Islam spread primarily by economic imposition is inaccurate. The empire's tolerance and the genuine appeal of Islamic teachings played a significant role in its spread across diverse regions during its expansion.