This is a very complicated question, so the answer is going to be quite long. Bear with me.
Colonialism is different from settler colonialism is different from arab conquests. Settler colonialism, for example, would be South Africa and the US (and Israel.) That is the kind of colonialism that had a profound effect on the ethnicity of the local population, usually requiring ethnic cleansing or apartheid and is what people somehow assume happened to the middle east and north african region back in the day.
European colonialism, when it wasn’t settler colonialism, was different because it was after the industrial revolution and they sought to strip colonised countries of their resources at the cost of the local population, as well as forcibly replace their indigenous culture and the rest of the White Man’s Burden crap, with a strong racial element. But the main interest was first and foremost resources and means of production, including land (but not for living! Africa is hot and dusty and gross) and labor.
Arabs had less interest in resources and spreading their culture (which was, by the way, quite sparse at the time.) The number one priority for the Muslim empire once the Prophet had died was maintaining security and power. Religion was a big part of it because Islam was a community-based religion that united previously separated Arab tribes under monotheism, and this also meant allegiance to the rising Muslim/Arab empire was largely a political thing, not a religious thing. And so the two main goals for Arab conquests were 1) maintaining security and preventing divisions amongst themselves and 2) spreading the word of Islam.
Now we’ll get to the security part in a second, but Islam was never spread forcibly. A good example of that is Egypt, which was already occupied by the Byzantines. The Arab army overthrew the Byzantines and came to an agreement with the Pope at the time, and Egypt remained a Coptic country for quite a while after that.
It’s true, however, that Islamic conquests made being a Muslim more convenient for nations under their authority, for trading access, political and tax purposes and for that reason (amongst others) Islam spread regardless. Arabic spread alongside mainly because scholars refused to translate the Qur’an, and so wherever Islam went, so did Arabic. That’s not to say it was a pain-free process and it certainly had an effect on religious minorities in the region, but it also cannot be equated to “colonisation.” The purpose of Islamic conquests was not to forcibly convert anyone (which went against the theology of Islam), and as for “systematically putting it instead of indigenous cultures” it was more like “inclusion into an existing empire,” which had already happened to every country in the region - whether from Greek, Roman, Byzantine or Sasanian empires. The Arab empire was not an unprecedented example of countries being under another regime’s authority. That’s the way things worked. This inclusion into various empires usually affected the ruling class more than anyone else; the rest of the population remained more or less the same.
Now back to security, which is the big one: the only way for Arabs to maintain security as the empire expanded was to create alliances with neighbouring countries, such as the Syrians and the Yemenis. Once Mu’awiya rose to the Caliphate, and the Umayyads rose to power, the center of Arab culture changed from Mecca and Medina to Damascus. The Abbasid Empire would later choose Baghdad as a capital. All of these changes were huge paradigm shifts for Arabs and the understanding of “Arab culture.” Where the Arab empire had once been an excluded, jealously guarded succession of families in tribes, the Abbassid empire marked a period of almost unprecedented cultural exchanges. The Iranization of the empire would have an influence on the way of thinking, feeling and writing. Caliph Ma’moun would order the translation of Greek work, notably philosophy, into Arabic, which would lead to a rapport between Arab thought and Greek thought. Arabs would become leaders of worldwide innovations in medicine, math, philosophy and music. Most notably, the creation of an Islamic empire during the Umayyad and Abbasid dynasties changed the worldview of Arabs because it changed the denotation of Arabs. Egyptian, Syrian, Mesopotamian, Yemeni and reluctantly Persian culture contributed to Arab culture as more populations identified as Arab, under the spread of Islam.
To quote Osama
, “the Islamic Empires were built on the backbone of non-Arabs, and the rule of “Arabs” over much of what is, today, defined as the Muslim World was seldom in the hands of Arabs.
Salah Ad-Deen and his Ayyubid descendants were Kurdish, the Ottomans were Turkish, Muhammad Ali was Albanian, the Mamluks were Eastern Europeans and Turks, and many of the Emirs and Sultans who ruled of city states were from a veritable bricolage of ethnicities.”
So really it is impossible for Arabs to have forcibly replaced anyone’s culture because their own
culture was the most flexible, and the one that changed the most. And Arab “colonisation,” Arabization - all of this is a singular term grouping a very diverse and very long period of history under a monolithic, reductive title. Nobody was Arab then, people just belonged to different empires. There were a lot of wars, a lot of cultural exchanges and erasure, and a lot of religious disruption. But it cannot be equated to European colonialism. That’s why they are referred to as “conquests,” and why it is fundamentally erroneous to refer to them as “colonialism.”