We shall reply this query by going back still further. As per the holy Qur’an, the aim of prophets, messengers, divine saints and reformists is that“men conduct themselves with equity” . (Chapter Hadid, verse 25) They rise up to establish justice. This rising would be widespread and universal only during Hazrat Mahdi’s time and by his hands.
So the ultimate aim of the Prophets and Imams is to create such an atmosphere in the entire world wherein all the people turn monotheist and pure Muslims and the cry:“There is no god but Allah; Muhammad is the messenger of Allah; Ali is the Wali of Allah” rings throughout the world. This is the ultimate aim. This hope and aspiration has remained unfulfilled right from the time of Hazrat Adam (a.s.) till the last prophet’s (s.a.w.a.) era though all the prophets and the last prophet did prepare its background to some extent.
The Imams (a.s.) have strived on this path and the reformists, preachers, writers and poets have been active too. However, as of today, justice and monotheism (where Allah has promised that these would become universal) have not yet become widespread. The person in charge of this vital task is the twelfth Imam, Hujjat-ibn-l’Hasan (a.t.f.s.). His introduction has come down in the holy Qur’an and Shia traditions, as well as, in numerous Sunni traditions. (the Sunnis accept the doctrine and originality of Mahdaviyat though they have not set forth some of Hazrat Mahdi’s precise characteristics)
To sum up, the ultimate aim of mankind, right from the beginning of existence is to see through Imam Mahdi’s rule and government. All along, all religions, groups and intellectuals have had hopes and aspirations in some way or the other.
When Hazrat Mahdi (a.t.f.s.) will rise to establish the universal government, a group will stand to oppose him out of ungratefulness and egoism and will create obstacles on his path. What is the remedy? What does reason command? Should this human hope and aspiration remain unfulfilled and instead turn into despair just for the sake of these few individuals!? Its here that defense and war (but after finalization of argument and call for peace) becomes necessary so that Hazrat can easily rule.
To achieve this aim, he has no alternative but to wage war. But it isn’t true that right from the beginning of this advent, he would start killing his opponents with the sword. For long, he will call the people towards Islam and Qur’an. The period of stability of his government would take a long time. By period of stability, we mean the period during which Hazrat would acquaint the people. The first sentence that he would utter is:
بقيةٍ الله خيرٍ لكم ان كنتم مؤمنين و انا بقيةٍ الله
Such a kind invitation shows that like his great grandfather, he too is an ocean of kindness and mercy. After he presents the true Islam to all nations and tribes and completes the argument for them, he will inevitably draw his sword against the stubborn enemies. This is because stability of Imam’s government is Allah’s indispensable Will and so, after finalizing the argument, he must inevitably fight against the enemies of monotheism and justice.
Actually, I have not seen any tradition pinpointed at the beginning of this query, nor did I find any by a short glance.
On the other hand, it has come down in numerous traditions that Hazrat Mahdi (a.t.f.s.) is victorious by the fear and is assisted and confirmed (by Allah). (fear would overtake all the governments and his government would be assisted by Allah). By reflecting over the traditions, any sound mind and pure heart will accept that defense and war is inevitable.
Thirdly, we can say that such type of traditions is applicable to the period just before Imam’s reappearance because it has come down in certain traditions that just before his reappearance, several wars would take place and numerous people in the world would get killed.
Imam Sadiq (a.s.) said,“Before the rising of the “Qaem” , there would be two deaths: The red death and the white death; such that five out of seven would perish. The red death is the death by sword (war) and the white death is plague.”
Consequently, if its war and destruction of human-beings, it would occur before reappearance. This too is a sign of reappearance but capable of divine alteration.
Hazrat would rise with the sword of his grandfather, the holy Prophet (s.a.w.a.), and after inviting the people he would fight just a few who wish to stand against the truth.