Every creature defends his life as well as his interests. Like others, every creature is equipped with a defensive power that enables him to combat with his enemies. With his Allah-given instinct and nature, man believes that he must defend himself and destroy the enemy who wants to destroy him and who never gives up his animosity.
He also believes that he should defend his rights if someone transgresses upon his vital interests and that he should cut off the hands of the transgressor by any means possible.
This natural phenomenon, which is invariably present in the nature of an individual, is firm and stable in human societies as well, i.e., an enemy who threatens the members of a society or its social independence is condemned to death by that society. This way of thinking has always been predominant in human societies that individuals and societies can make any decisions and can act harshly against their dangerous enemies.
Islam is also a social religion established on the basis of Tawhid. Islam considers those who refuse to abide by truth and justice as its vital enemies and as the ones who disturb the order of humanity. Islam does not believe in any human value and respect for them.
Since Islam is itself a universal religion and because it has not set any specific place as its homeland and frontiers for its followers, it fights with anyone who believes in shirk and who does not accept the truth and divine laws by clear logic and wise counsel in order to make him follow truth and justice.
The essence of the laws of Islam on jihad is only this and no more. It is exactly in accordance with the policies which are usually adopted by every human society against its vital enemies.
Contrary to the propaganda by the malicious enemies, Islam is not the "religion of sword", for Islam is not an imperial-plan which knows no logic but sword and political maneuvers, rather it is a religion whose founder is Allah Who, in His Divine Words, addresses the people through logic and reasoning and invites His creatures to a religion which corresponds to their creation.
A religion whose general initial greeting is salam (peace) and whose universal policy, according to the explicit wording of the Holy Qur'an, is: ('''') "...Reconciliation is better ...(4:128)" will never be a religion of sword and oppression.
During the lifetime of the Holy Prophet (S), when the divine light of Islam had illuminated the entire Arabian Peninsula and when Muslims were involved in important battles and severe wars, the casualties of the Muslims did not reach more than two hundred persons and the casualties of the unbelievers did not touch the figure of one thousand in number. (Among these one thousand people, seven hundred belonged to Banu-Qurayzah, who were killed by the order of the arbitration they had themselves chosen.). Thus it is quite unfair to call such a religion, the "religion of sword".

The Instances of War In Islam
There are a few groups with whom Islam combats:
(1) Mushrikin: These are the ones who do not believe in Tawhid, Nubuwwah, and Ma'ad. This group should primarily be invited to embrace Islam. The facts of religion must be explained to them clearly in such a way that no ambiguity and excuse would remain. Then if they accept these truths, they will be considered as the brothers of other Muslims and equal to them in profits and losses. But if they refuse to accept the truth and reality after these are clearly explained to them, Islam will perform the religious duty of jihad against them.
(2) Ahl al-Kitab: These are the followers of the Divine Books [6] who have a religion and a divine book from the viewpoint of Islam and who believe in Tawhid, Nubuwwah, and Ma'ad. Islam gives its permission to these groups to live under its protection by paying jizyah (head tax charged from Ahl al-Kitab in lieu of their non-acceptance of Islam), that is, - by accepting the guardianship of Islam, they must safeguard their own independence and perform their deeds according to their own religious regulations.
Their life, honour, and property will be respected like that of all other Muslims. In lieu of this, they must pay an insignificant sum as jizyah to the Muslim society. They must not, however, make evil propaganda, help the enemies of Islam, or perform anything else that is to the detriment of the Muslims.
(3) Those who do injustice and engage in corruption: This group of people includes those Muslims who engage in armed rebellion against Islam and the Muslims and embark on the massacre of other Muslims. The Islamic society combats with such people, so that they may surrender and give up corruption and revolt.
(4) The enemies of Islam who attack in order to destroy the very foundation of Islam or to overthrow the Islamic Government: In this case, it is wajib for all Muslims to defend Islam and to deal with them like kafir harbi(unbeliever to be fought against).
If it is deemed advisable in the interests of the Muslims and Islam, the Islamic society can temporarily enter into a non-aggression treaty with the enemies of Islam, but it does not have the right to establish friendly relations with them in a manner that their words and actions cause evil effects and corrupt the thoughts and deeds of Muslims.

Escaping From Jihad and Defence
Running away from the battlefield and escaping from the enemy means that the person who runs away considers his life as more valuable and dearer than the existence of the society. It is indeed the surrender of religious sanctities and the life, honor, and property of the society to an enemy who threatens their lives in all respects.
Therefore, escaping from jihad and defense is a mortal sin. The Almighty Allah has explicitly promised to put the person who escapes from jihad in hell as He states: "And whoever shall turn his back to them on that day unless he shall turn aside for the sake of fighting or withdraws to a company - then he, indeed, becomes deserving of Allah's wrath, and his abode is hell...(8:16)."

Defending the Islamic Domain
According to what has been discussed, defending the Islamic society and the territory of Muslims is one of the most important Islamic obligations. The Almighty Allah states: "And do not speak of those who are killed in Allah's way as dead; nay, (they are) alive, but you do not perceive (2:154)".
The story of men who most heartily participated in bloody battles during early period of the advent of Islam and of martyrs who got weltered in their pure blood is extremely astonishing as well as exemplary. These were the ones who established and made firm foundation of this holy religion with their pure blood and severely injured bodies.

Fighting With the Internal Enemies of The Society
As according to natural logic, we ought to fight the foreign enemies and defend the society from damages, we should combat and fight the internal enemies of the society as well. The internal enemy of the society is one who breaches the general policies and the rules that are in force and thus disrupts and deranges the general order of the society. That is why security forces and various punishments to retribute the offenders are established in organized societies to safeguard the order and continuation of affairs.
In addition to setting up the executive power and various punishments, Islam has made incumbent upon all individuals to carry out the precept of al-amr bil-ma'ruf (enjoining the lawful acts) and al-nahy 'an al-munkar (forbidding the sinful acts), thus making the campaign more general and more effective.
The main difference between Islam and other social policies is that other policies have only focused on the reformation of the actions and deeds of the people, but Islam has paid attention to both actions and ethics of the people and has fought against corruption in both the instances.
Sins which have been forbidden by Islam are the actions that have sinister effects and evil consequences in the society. Nevertheless, some of these sins directly corrupt the individual or individuals who commit them and somehow influence the society as local wounds and organic complications that appear in the human body. Most sins, such as not reciting salat and not observing sawm, disturb the status of worshipping Allah and deny the divine rights and so fall within this category.
Some of the sins directly threaten the social life and annihilate the whole structure of the society like diseases which directly affect human life and disrupt the affairs of man's life. Lying and slandering fall under this category. According to Islam, the rights of parents, backbiting, and attacking the honor of the people also fall under the same category.

Defending the Truth
Another defense which is much more profound and enormous than defending territory is the defense of right which is the only objective of the holy religion of Islam. The most important aim of this divine policy is the revival of right and reality and hence this pure religion has been named as the religion of truth, i.e., a religion that belongs to the truth, involves nothing but the truth, and aims at nothing but the truth.
While describing about His Book, which contains all the truths, the Almighty Allah states: "...Guiding to the truth and to a right path (46:30)."
That is why it is incumbent upon every Muslim to follow the truth, tell the truth, listen to the truth, and defend the truth with his utmost capacity and in any way possible.