As explained in the first part of the topic, Islam has spread much more quickly compared to other religions all over the world. The traits of Prophet Muhammad (PBUH&HP) were introduced as one of the reasons. Here, the effect of the scientific and social interactions with the rest of the world throughout the Islam's history is discussed. 

 As an introduction, it is good to know that Islam has adopted two types of regulations; confirmed rules and established ones. The Islamic approach regarding the confirmed rules -the regulations which existed before and were conserved or revised if needed- is one of the keys to the development and permanence of Islam. And, this will be the focus of this article.   

Saying Yes to the Good Costumes throughout Islam's History

The Islamic approach to the habits and rules that were common in the pre-Islamic era was that it neither opposed them totally nor accepted them entirely. In some cases, Islam has affirmed and preserved some rules. That was when those rules or customs were not in contradiction to the social order and the living facilities of humans or in case of the righteous customs and traditions that existed before the emergence of Islam; e.g., some of the rules on making contracts. 

However, some of the useful regulations required to be revised and this was accomplished by adding some conditions. On the contrary, some customs and routines were opposed and removed due to the bugs and disadvantages or because they were manipulated or misused for personal benefits; e.g., usury (Riba) [1].

The rules conserved by Islam, such as those about the ownership and property, are called confirmed rules. On the other hand, the rules instituted by the Islamic jurisprudence which never existed before are called established rules [1]. This demonstrates that Islam has always been in constant interaction with the world, and the positive aspects of human societies are considered. Hence, the message of Islam and its framework have not been far from what people are familiar. This consequently has made it easier to accept Islam.

Seeking knowledge; A Way to Spread Islam

Islam has urged everyone to seek knowledge. The first verse of the Quran revealed to Prophet Muhammad (PBUH&HP) enjoined reading which is the key to knowledge: “Read in the Name of your Lord who created” (96:1). Literacy and having knowledge are so important in Islam that Quran equals illiteracy to being in darkness. According to Prophet Muhammad (PBUH&HP), seeking knowledge is obligatory (Wajib) for every Muslim and God loves those who seek knowledge [2].

Learning and seeking knowledge have been emphasized such that Muslims have been encouraged even to travel in order to learn things. Imam Ali (AS) recommended traveling to acquire privilege and named gaining knowledge as one of the achievements of traveling [3]. Prophet Muhammad (PBUH) advised seeking knowledge even if for that purpose one should go to the lands far away [4].

The Holy Quran also addresses the believers as those who are not affected by the wrong behaviors of others since they have been guided. So, the believers can peacefully learn from the positive aspects of others. Another proof of the attention paid to knowledge in Islam is that Muslims used to release the prisoners of wars who taught literacy to a certain number of Muslims. All these emphases and recommendations have urged Muslims to travel to gain knowledge. As a result, Muslims who traveled to other places and countries were practically the messengers of Islam there, which, in consequence, accelerated the spread of Islam.

Continuous interaction with the world During Islam's History 

The actual advances all over the world are the outcomes of the efforts that various nations and civilizations have made in the course of time, among which are the Islamic civilizations [6]. Muslims in different countries, like Spain and Italy, have always been in interaction with other people; therefore, they could transfer the Islamic civilization and culture to others and also receive from them. As an instance, in the battle of the Trench (Khandaq), Salman Farsi proposed to dig a trench around Medina.

This was a tested strategy in Persia, and Prophet Muhammad (PBUH&HP) accepted it. Many of the important Arabic resources and books were translated into European languages, some of which were later on taught and used as references in scientific centers in non-Muslim countries. The bonds between Muslims and Christians through marriage [i] and social relationships were of other means to expose non-Muslims to Islam [7]. All these factors have helped the quick spread of Islam.

From what has been discussed, we can see that the Islamic approach of making regulations under the form of confirmed rules, the encouragement to obtain knowledge and literacy, and cultural exchanges with the rest of the world played significant roles in attracting many savants and people to the religion of Islam.    

Notes:
[i] This kind of marriage named Interreligious marriage is permitted in Islam under the certain conditions. 

References:

1. spreading Islam
2. “Misbah al-Shariah”, p. 13.
3. M. Nuri, “Mustadrak al Wasail”, vol. 18, p. 115.
4. “Misbah al-Shariah”.
5. “Ghurar al-Hikam wa Durar al-Kalim”, p. 46, T. 188.
6. history of Islam
7. A. Velayati, “Dynamism of Islamic and Iranian Culture and Civilization”, vol. 1. 

In Islam, there are some ceremonies and occasions which are held all around the world among Muslims. They all have religious backgrounds and are mostly referred to in the holy Quran. Muslim nations have been commemorating them in the course of history. Here we are going to have a glance at the most significant Islamic occasions based on the Lunar Calendar.

6 Major  Islamic Occasions 

1.10th of Muharram: Martyrdom of Imam Hussain (AS)

The month of Muharram is the first month of the year in the lunar calendar. On the tenth day of this month, Hussain Ibn Ali (AS), the grandson of Prophet Muhammad (PBUH&HP), and his companions were brutally martyred, and their women and children were taken captive by the caliph of the time, Yazid ibn. Muawyah. Their story has been the source of inspiration for many new converts. 

2. 20th of Safar: The Day of Arbaeen

Arbaeen is the Arabic word for forty, and it marks the 20th of Safar, the fortieth day after Imam Hussain's (AS) martyrdom on the day of Ashura, who was martyred in the event of Karbala along with his companions in the cruelest and most inhumane way possible. 

According to some historical accounts [2], some of the members of Imam Hussain's (AS) family after being released from the bondage of Yazid's forces returned to Karbala from Sham (today's Damascus) to visit Imam Hussain's (AS) grave. Also, some believe that Imam Hussain's (AS) head, which was taken to Sham by Yazid's army was brought back to Karbala on this day and buried with his body [3] & [4]. 

Every year, a few days before this day, a vast number of people from all over the world, Muslims or even non-Muslims, gather in Iraq to take part in a symbolic walk, to revive the teachings of Imam Hussain (AS) and commemorate his sacrifice in the way of Allah and humanity. 

3. 17th of Rabi al-Avval: Prophet Muhammad's (PBUH&HP) Birthday

There is a disagreement concerning the exact date of Prophet Muhammad's (PBUH&HP) birthday. Some believe it occurred on the 12th of Rabi al-Avval, while others consider it to be on the 17th of Rabi al-Avval, the third month in the Islamic calendar. Prophet Muhammad (PBUH&HP) was born in Mecca. All Muslims around the world celebrate his birthday and regard it as one of the important Islamic occasions. On this day, Muslims feed the needy, pray and recite the Quran, commemorate Prophet Muhammad (PBUH&HP), and his challenges to deliver the messages of Allah to human beings.

4. 1st of Shawwal: Eid al-Fitr

The first day of the month of Shawwal, the tenth month of the Islamic calendar, is called Eid al-Fitr. After fasting for one month, during the month of Ramadan, remembering, worshipping Allah and trying to do fewer sins beside not eating and drinking from before the Call for Fajr prayer to after the Call for Magrib prayer, Muslims celebrate the first day of the month of Shawwal, for their success in submitting to Allah's command. They perform the Eid prayer first; then, they hold a feast inviting their loved ones, wear their best clothes, and visit their friends and family. The culture of feasting might be different in different Islamic communities, but one thing is for sure; no one is allowed to fast on this exceptional day. Allah also obliges Muslims to share their blessings and happiness with the needy with the money they donate to them. 

5. 10th of Dhu'l-Hijjah: Eid al-Adha

Eid al-Adha is one of the most significant Islamic occasions. Some of the most important events of this Abrahamic religion happened on this day. On this Eid, similar to Eid al-Fitr, Muslims are not allowed to fast. The first is the sacrifice of Ishmael by his father, Abraham, for the sake of Allah. When Abraham and his son both surrendered, and he was ready to behead his son, Allah sent a ram and asked Abraham to kill that instead.

"So when they had both surrendered [to Allah's will], and he had laid him down on his forehead, We called out to him, 'O Abraham! You have indeed fulfilled your vision! Thus indeed do We reward the virtuous! This was indeed a manifest test. Then We ransomed him with a great sacrifice, and left for him a good name in posterity." (37: 103-108)

This day is also the last day of Hajj rituals, in which Muslims shall sacrifice an animal to feed the needy Muslims. On this day, those who attended Hajj have performed all their Hajj rituals, and with the great assistance of Allah, all their sins are wiped away, and Allah accepts their good deeds and repentance.

Many Muslims celebrate this day. They sacrifice an animal to feed the needy, even if they have not attended Hajj. If they do not have enough money to buy a sheep, they do other things and feed the destitute in different ways. This sacrifice is an expression of generosity and obedience to the commands of Allah. This Eid also reminds humankind of the characteristics, such as envy, rage, dishonesty, etc., they have to symbolically sacrifice in themselves to become the better version of themselves and be worthy of being Allah's best creation. 

5. 18th of Dhu'l-Hijjah: Eid al-Ghadir

This Islamic occasion was a day in the last Hajj pilgrimage (Hajjat al-Vida'a) of Prophet Muhammad (PBUH&HP). When he was going back to Medina with all his companions and other pilgrims, he gathered everyone around a place called Ghadir and announced these words in which he appointed Imam Ali b. Abi Talib (AS) as his caliph and the Imam after himself following a direct order from Allah [i]:

"Whomsoever, I am his leader (Mawla), Ali (AS) is also his leader (Mawla). O' Allah! Love those who love him (Ali (AS)) and oppose those who oppose him" [1]

This is another important day in the Muslim calendar. On this day, Muslims can fast and again feed the needy, as an essential part of Islamic culture. 

These are the most significant and most celebrated Islamic occasions. As one can see, feeding others and praying to Allah are the essential things a Muslim should do to celebrate a feast, which reveals the importance of caring for others in Islam that results from the devotion to Allah.  

Notes: 
[i] Verse 67th of Surah al-Maedah known as Al-Tabligh Verse, and the third verse of the same chapter known as Al-Ikmal Verse. 

References:

1.  Ibn Athīr, Usd al-ghāba, vol. 3, p. 605; Kulaynī, al-Kāfī, vol. 1, p. 295; Balādhurī, Ansāb al-ashrāf, vol. 2, p. 110-111;
2.  Ibn Tawus, 'Ali b. Musa, Al-Luhuf 'ala qatla l-tufuf, Uswi, Qom, 1414 AH.
3.  Al-Biruni, Abu Rayhan, The Remaining Signs of Past Centuries, p.331.
4. Qazi al-Tabataii, Muhammad Ali, A Research on the first Arba'een of the Leader of Martyrs (Imam Hussain (AS)), vol.3, p.304.