When facing a question like this, you may find a group of people who try to justify that Islam is not a religion of peace. They usually refer to terrorist attacks by pseudo-Muslims and conclude that Islam is not a peaceful religion. Peace in Islam is a value and an ultimate goal of life; may it be personal, social or worldwide.

But let’s see what is Islam’s viewpoint about war and if it approves terrorism.

What Do We Mean by Peace in Islam?

Before discussing the main topic of this article, we have to understand what peace in Islam means. According to Merriam Webster dictionary, “peace is a state of tranquility or quiet such as:

Freedom from Civil Disturbance
A state of security or order within a community provided for by law or custom.
Freedom from disquieting or oppressive thoughts or emotions 
Harmony in personal relations.” [1]

Therefore, there are two types of peace defined above; social and individual. Islam not only talks about individual peace, but also all of its rules are based on logic to shape a peaceful society. In this article, we would focus on social aspects of peace in Islam, either within one country or on what goes on between different countries.

Peace in Islam

Allah emphasizes in the Quran that Prophet Muhammad (PBUH&HP) is a mercy towards all human beings: “We did not send you but as a mercy to all the nations” (21: 107). It can be understood from this verse that a worldwide mercy, peace, and tranquility is the goal of sending Prophet Muhammad (PBUH) with the religion of Islam.

Imam Ali (AS) in his letter to Malik al-Ashtar (his appointed commander in another country) wrote: “Develop in your heart the feeling of love for your people and let it be the source of kindliness and blessing to them. Do not behave with them like a barbarian, and do not appropriate to yourself that which belongs to them. Remember that the citizens of the state are of two categories. They are either your brethren in religion or your brethren in kind. They are subject to infirmities and liable to commit mistakes.”  [2]

He specifically notes that we should be tolerant of people who have no bad deeds against Muslims and the religion of Islam.

Are Muslims Peaceful towards Everyone?

In social relations The Quran defines Muslims as moderate people; “Muhammad, the Apostle of Allah, and those who are with him are hard against the faithless and merciful amongst themselves. “ (48:29)

By referring to the above verse and by going through its interpretations we find out that “Muslims should be harsh on infidels. Who are these infidels? Muslims should not be harsh on anyone who does not believe in Islam. They should behave kindly towards those who are not opposed to them, who do not plot against them, and who do not seek to wipe out their nations - even if they follow other faiths.” While at the same time “Muslims should be harsh on those who fight against Islam and their identity, nationality, country, independence, honor, dignity, traditions, culture, and values.” [3] Therefore, it is completely rational for Muslims to defend themselves while their values are being attacked, and it has no contradiction with their peaceful nature.

Does Islam Allow Terrorist Attacks?

In recent years we have seen different terrorist groups such as Taliban, Al-Qaida or ISIS, who under the name of Islam, have committed terrorist attacks in different countries. They refer to verses of the Quran that are about the holy struggle (Jihad) and use those verses as a permission for their terrorist acts.

However, their interpretations of the verses of the holy struggle (Jihad) are not correct. The fact is that war is prohibited in Islam, and Muslims are not allowed to start a war against other countries for the sake of conquest or even for spreading the religion of Islam. Jihad is allowed for Muslims only if:

They are attacked by other countries, and their lives and properties are at risk.
If other Muslim territories are under attack by oppressive governments.
If other powers attack Muslim territories to annihilate Muslims or their religion.

“In the holy struggle (Jihad), violating or infringing on others' rights is not allowed. Killing other people under baseless pretexts is not part of the holy struggle (jihad). Neither is killing those who are not Muslims. Such acts are not allowed in the holy struggle (Jihad). Not all those who believe in religions other than Islam should be treated with harshness. Rather, only those who are opposed to Islam, your independence and territorial integrity, and Islamic culture, identity, and values should be treated with harshness. If carried out under these conditions, the holy struggle (Jihad) is considered as a divine order and will bring about glory to nations.” [4]

It is only under these conditions that Muslims are allowed to fight against the oppressors. And even when they are allowed to defend themselves and enter the war, they have to make sure to follow the rules of war. They are not allowed to kill the children or elderly of the infidels, or to poison the cities of the infidels. [5]

They have to tolerate the refugees, and if they betray them, they will face punishment [6]. Also, they should observe the rights of the captives of war [7]:

“Allah does not forbid you from dealing with kindness and justice with those [polytheists] who did not make war against you on account of religion and did not expel you from your homes. Indeed Allah loves the just. Allah forbids you only regarding those who made war against you on account of religion and expelled you from your homes and supported [the polytheists of Makkah] in your expulsion, that you make friends with them, and whoever makes friends with them—it is they who are the wrongdoers.” (60: 8-9)

Islam Is a Peaceful Religion, not a Passive One

In conclusion, Islam is a religion of peace for Muslim people and peaceful people. It is not a passive religion to sit and watch all the cruel things that are happening in the world and smile at it. Islam is the life map for those who wish to reach human perfection which is only achieved by obeying all of its rulings. No matter you call it Islam or something else, but every sane human being, by studying The Quran and searching about Islam, will understand that Islamic rules have been designed to make the society a safe place for human growth.

References:

1. peace
2. Malik Ashtar richest treasure
3. view of Jihad
4. ibid
5. Mafatih al-hayat, p. 318
6. Mafatih al-hayat, pp. 419- 20
7. Mafatih al-hayat, p. 423

Imam Jawad (AS) is the ninth Shiite Imam. His father is Imam Reza (AS), and his mother’s name is  Sabikah. His original name is “Muhammad,” but his epithet is “Jawad,” meaning “a very generous person.” He was born on 195 H (810 AC) in Medina. (1)

Generally, Shiite Imams carried prestige among their tribe and were respected by everyone. Many Shias believed that Imams were merely knowledgeable people who gained their knowledge only from their ancestors and they were not extraordinary. However, the imamate of Imam Jawad (AS) made all the Shias think differently and change their minds. He was only eight years old, when his father, Imam Reza (AS), was martyred. According to hadiths, the earth cannot be without an Imam. Accordingly, Imam Reza (AS) said:
The earth cannot be without any of us, Imams, whether he is known by the people or hidden from them. (2)

Shias didn’t know who would be their leader after Imam Reza (AS). But, he introduced Imam Jawad (AS) as his successor (3) and showed the Shias that “Imam” was not an ordinary person and he could be the leader of the whole Shias despite being young. 

Knowledge is a sign of imamate 

The hadiths suggest various signs for Imams so that we can differentiate between the truly chosen Imams by Allah and impostors. One of the most significant signs is that he is the most knowledgeable person of his time. 

Prophet Muhammad (PBUH & HP) said:
Do not try to teach something to Ahlul Bayt because they are far more knowledgeable than you. (4)
Regarding this, Imam Sadiq (AS) acknowledged:
Indeed Ali (AS) was a knowledgeable person whose knowledge will be passed to his successors and no knowledgeable person (an Imam) dies except to leave their knowledge to someone else. (5)
He also said:
The successor of an Imam attains the knowledge of the previous Imam in the last moment of his life. (6)

The debates of Imam Javad (AS) with religious scholars

Ma’mun was one of the Abbasid Caliphs who lived during the same period as Imam Reza (AS) and Imam Jawad (AS). During his caliphate, the Shia population increased dramatically which intimidated him. Due to this fact, he lied that Imam Reza (AS) was his successor and led people to believe that he was not an enemy of Shiite Imams. But at last, he killed Imam Reza (AS). After Imam Reza (AS), Imam Jawad (AS) was his most important enemy. He made Imam Jawad (AS) marry his daughter so that he could deceive people longer. 

Many of the Abbasid royalties were against Ma’mun’s decision, as they believed that the boy was too young and he wasn’t a knowledgeable person. Ma’mun proposed that they should test the knowledge of Imam Javad (AS), in order to show everyone how extraordinary he is. Imam Javad (AS) was only nine years old at that time. 

One of the most knowledgeable religious scholars in those times, Yahya ibn Aktham, volunteered to have a discussion and debate with Imam Javad (AS). 
During the discussion, Yahya ibn Aktham asked Imam Javad (AS) about a person who has killed an animal while making Hajj; what should he do? (During the Hajj ceremony, it is forbidden for the pilgrims to kill any creature).
Imam Jawad (AS) said that it depends: Did he kill it in Mecca or outside of it? Did he know about this law or not? Has he done it intentionally or unintentionally? Was he free or was he a slave? Was it his first time? Was it a bird or something else? Was it a small animal or a big one? Is he ashamed of what he did or not? Did he do it at night or during the day? Was it Umrah (a special type of Hajj) or regular Hajj? 
Yahya was so surprised that he couldn’t answer the twelve questions of Imam Jawad (AS), but instead, Imam Javad (AS) answered them one by one and explained the rules to everyone. 
Ma’mun told people that “Now do you see what I was telling you?” (7)
During another session, Yahya asked Imam Jawad (AS) about a hadith from the Prophet (PBUH & HP) that Sunni narrators had recorded. The hadith said “Once Gabriel came to the Prophet (PBUH & HP) and told him ‘O Muhammad! Allah told you to inform Abu-Bakr that I am satisfied with him. Is he satisfied as well?” Yahya questioned Imam Javad (AS) about the authenticity of this hadith.
Imam Jawad (AS) said, “I do not deny the privileges of Abu-Bakr … but this hadith is contrary to the verses of the Quran.” Imam Javad (AS) stated he wouldn’t deny the privileges of Abu-Bakr because he was surrounded by Sunnis and it was so dangerous for him to speak out against Abu-Bakr.
Then he said, “The holy Quran says 
‘Surely We have created man, and We know the promptings of his heart, and We are nearer to him than even his jugular vein.’ (50:16) 
Then why should Allah ask Abu-Bakr whether he is satisfied with him or not while Allah already knows it?”
Yahya referred to another hadith that claims Abu-Bakr and Umar on the earth are like Gabriel and Michael in the skies. 
Imam Javad (AS) said “This hadith cannot be accepted as well, because Gabriel and Michael never worshiped anyone except Allah, while Abu-Bakr and Umar spent most of their lives as polytheists and worshippers of idols.” 
Yahya added that Abu-Bakr and Umar are the lords of the elderly in Paradise.
Imam Javad (AS) stated that it is impossible as people in Paradise are all young not old. Umayyad dynasty made this fake hadith because they didn’t like the authentic one narrated by the Prophet (PBUH & HP) that reads, “Hassan (AS) and Hussain (AS) are the lords of young people in Paradise.” (8)
Yahya said it also has been narrated that Umar is the one who illuminates Paradise.
Imam Javad (AS) responded that it is also impossible. Do you think that Paradise is not illuminated by the Angles and Prophets like Adam (AS) and Muhammad (PBUH & HP) but rather by Umar?!
Yahya said it has been claimed that the angels talk with the tongue of Umar.
Imam Jawad (AS) said that he does not deny the privileges of Umar. However, Abu-Bakr was better than Umar as he said, “I have a Satan that sometimes tempts me, so if you see me deviating, stop me.” 
Yahya asked many other questions about Abu-Bakr and Umar, and Imam Javad (AS) answered them all. (9)   
Not only Imam Javad (AS) did not fail to answer the questions, but also, he posed more questions that even the most knowledgeable scholars felt incapable of disputing with Imam Javad (AS). These debates happened when Imam Javad (AS) was only 8 or 9 years old. 
As it might be apparent, Shiite Imams were extraordinarily knowledgeable, and their knowledge was given to them by God not by learning in classes and the like. They were the most knowledgeable individuals in their era regardless of their age.

Resources

1.  I’lam al-Vara, Sheikh at-Tabarsi, vol.2, pg.91
2.   Kamal ad-Din, Sheikh Saduq, vol.1, pg.202
3.  Al-Kafi, Sheikh Koleini, vol.1, pg.320
4. Mu’jam al-Kabir, at-Tabarani, vol.5, pg.166
5.  Al-Kafi, Sheikh Koleini, vol.1, pg.221
6.  Al-Kafi, Sheikh Koleini, vol.1, pg.275
7.  Al-Ih’tijaj, at-Tabarsi, vol.2, pg.444
8. Sunan al-Kubra, Nasa’i, vol.7, pg.460
9. Al-Ih’tijaj, at-Tabarsi, vol.2, pg.446-448