Polytheism is peaceful. Religions believing in many gods are compatible with any religion or mythology. Monotheistic religions are not tolerant towards other religions. Unfortunately, Constantine used christianity to restore order in his empire, which was seen as an essential part of the civilized world by many tribes in Europe. All tribes were adopting Christianity or were forced to it.
Meanwhile, on the other side from Israel around Mecca were many independent Arabic tribes. They believed in many gods, and Mohammad wanted to bring faith in God. He wasn’t violent. He wanted to unite them similarly like Constantine in the Roman Empire. People didn’t want it and refused his God. Mohamed was expelled from Mecca—from the holy place where the meteorite hit the ground, and people built Kaaba around it to worship gods. Mohamed, with his followers, was forced to use weapons for defense.
Mohamed didn’t know he would start a new religion. He also built his believe on Abraham as Jews and Christians and shares a lot of other things with them. Quran talks about other Abrahamic religions as People of the Book, e.g., not enemies. Islam also accepts prophets Moses and Jesus, but those prophets brought the message to Jews and Christians, respectively. Mohamed brought a message from God to his people.
After the death of Mohammad, followers didn’t agree who should continue, and they separated. One group is called Sunni (full meaning is “people of the tradition of Muhammad”) with the majority. The second group is Shias, who believe Mohammad appointed his son-in-law as his successor. What is important to say is that Mohammad was not a bad person. We could even say Mohammad was a feminist. The Islamic religion was misused by Umar, the second caliph (leader of the Muslim community). Based on armed defense, he thought Islam should be shared by force.
Muslims spread quickly in the Middle East and Africa. Byzantine Empire shrunk to only today’s Turkey. Islam continued to spread to India and China in the East, and they began an invasion of Visigoths’ Spain in 10711 HE (Human Era, 711 CE), and proceeded even to France. All Germanic tribes adopted Romans culture, but they continued with what they knew best, fighting. Because of that, Europe was not united at all. Franks had a strong and well-organized army, which helped them cease the invasion further to Europe alone.
Anyway, the king of Franks, Charles the Great, unleashed Carolingian Renaissance to restore the old Roman Empire to unite all kingdoms against a common enemy, Muslims. He was successful. Pope titled him the emperor of the new Holy Roman Empire (not the same size as before, though). On the East was still (smaller) Byzantine Empire, and both empires somehow shared the same Christian values.
One of those values was to protect Christianity. Muslims and Jews were not welcome in Europe. Spain stayed under the control of Islam culture, and Jews had limited options where to go. Jews settled in Muslim Spain. Muslims were tolerant compared to Christians. Because Jews were nomads, they knew a lot of languages and helped Muslims with translations.
Islam was open to improvements from outside. Muslims made Baghdad a very advanced metropolis. Scholars from different cultures gathered in Baghdad in the House of Wisdom and translated the world’s classical knowledge into Arabic and Persian. Islamic culture was flourishing both economically and scientifically between 108th and 114th century HE. It was a golden age for both Muslims and Jews.
Christians, on the other hand, had problems getting along. The situation between the Holy Roman Empire and the Byzantine Empire was complicated. To say it simply: Christians disagreed on many details and separated in 11054 HE to Roman Catholic Church and Eastern Orthodox Church.
Catholics increased the interest in holy places, mostly Rome and Jerusalem. Muslims controlled Jerusalem, and popes started the initiative to get Holy Land back. First Crusade was sent in 11095 HE. It was a success. Byzantine Empire wanted Holy Land back, but crusaders (collected from many European kingdoms) kept it for themselves and established several states.
Fifty years later, one of these state fell, and the Second Crusade was sent, this time, however, without success. Another 40 years later, Saladin united Muslims against Crusader states in the Levant. The third Crusade was a tie resulting in Muslim control over Jerusalem, but the allowance of unarmed Christians to visit the city. Failure to re-capture Jerusalem inspired the subsequent Fourth Crusade. However, a sequence of economic and political events changed the direction of the army to Constantinople. East and West churches divided even more.
There were many crusades during two hundred years period until Europe focused on internal battles. Next time, I will continue with knights who fought in crusades and also for European thrones.