“No real peace can be till the heart of man deserves peace; the law of Vishnu cannot prevail till the debt to Rudra is paid.” 
“The weakness of the human heart wants only fair and comforting truths or in their absence pleasant fables; it will not have the truth in its entirety because there there is much that is not clear and pleasant and comfortable, but hard to understand and harder to bear” 
Peace, you say? but what Peace?
Where better to begin on peace than the ancient Vedic message sarva janah sukhino bhavantu ? Translated simply: “let all people live in happiness through peace”. Indeed, the ideal of peace is felt by every Indian to be as old as India herself. But what is the kind of peace it refers to? A living or a dead peace? You can put a country to the sword and create a peace that is dead. You could have also a country emasculated or ruthlessly regimented (Communist regimes of the world for example), with a passivity or uniformity of mind, with no physical agitation, giving the appearance of peace, but really a state of death in disguise. Even a peace among free people cannot be a living one in the true sense of the word: an open conflict may be absent and still a selfish feud on the ideological level, and a self-interested economic throat-cutting continue.  Surely this is not the peace meant by sincere pacifists the world over and implied by the old phrase from the Rig-Veda 
National armies and Force
So long as national egoisms live and are held sacred and there is no final check on their inherent instinct of expansion, war will be always a possibility and almost a necessity of the life of the human peoples. If national armies exist, the possibility, even the certainty of war will exist along with them. 
And there is no chance of national armies being abolished; for each nation distrusts all the others too much, has too many ambitions and hungers, needs to remain armed, if for nothing else, to guard its markets and keep down its dominions, colonies, subject peoples. 
Is it reasonable at all then, to dream of a ‘world without war’? How does a clan, a state, a nation circumvent distrust? Would any self-respecting nation be willing to lay down its arms? Which country would want the superb distinction of being the first to stand bare on a field of armored warriors? Disarmament is good, and is a worthwhile cause, especially nuclear disarmament, but there remains a fundamental difficulty with these noble efforts – human nature.
While man remains what he is, force in spite of all idealisms and generous pacific hopes must remain the ultimate arbiter and governor of his life and its possessor the real ruler. 
Whenever a class or an opinion has thought itself oppressed or treated with intolerable injustice, has found the Law and its armed force so entirely associated with an opposite interest that the suspension of the principle of law and an insurgence of the violence of revolt against the violence of oppression were or appeared the only remedy, it has, if it thought it had a chance of success, appealed to the ancient arbitration of Might. Even in our own days we have seen the most law-abiding of nations staggering on the verge of a disastrous civil war and responsible statesmen declaring their readiness to appeal to it if a measure disagreeable to them were enforced, even though it was passed by the supreme legislative authority with the sanction of the sovereign. 
War and violent revolution can be eliminated, if we will, though not without immense difficulty, but on the condition that we get rid of the inner causes of war and the constantly accumulating Karma of successful injustice of which violent revolutions are the natural reactions. Otherwise, there can be only at best a fallacious period of artificial peace. What was in the past will be sown still in the present and continue to return on us in the future. 
The psychological necessity
So long as war does not become psychologically impossible, it will remain or, if banished for a while, return. War itself, it is hoped, will end war; the expense, the horror, the butchery, the disturbance of tranquil life, the whole confused sanguinary madness of the thing has reached or will reach such colossal proportions that the human race will fling the monstrosity behind it in weariness and disgust. But weariness and disgust, horror and pity, even the opening of the eyes to reason by the practical fact of the waste of human life and energy and the harm and extravagance are not permanent factors; they last only while the lesson is fresh. Afterwards, there is forgetfulness; human nature recuperates itself and recovers the instincts that were temporarily dominated. A long peace, even a certain organisation of peace may conceivably result, but so long as the heart of man remains what it is, the peace will come to an end, the organisation will break down under the stress of human passions. War is no longer, perhaps, a biological necessity, but it is still a psychological necessity; what is within us, must manifest itself outside.
Meanwhile it is well that every false hope and confident prediction should be answered as soon as may well be by the irony of the gods; for only so can we be driven to the perception of the real remedy.
Only when man has developed not merely a fellow-feeling with all men, but a dominant sense of unity and commonalty, only when he is aware of them not merely as brothers, — that is a fragile bond, — but as parts of himself, only when he has learned to live not in his separate personal and communal ego-sense, but in a larger universal consciousness can the phenomenon of war, with whatever weapons, pass out of his life without the possibility of return.
Meanwhile that he should struggle even by illusions towards that end, is an excellent sign; for it shows that the truth behind the illusion is pressing towards the hour when it may become manifest as reality. 
 From the chapter “Time the Destroyer”, [Book_3, p 386]
 from Essays on the Gita, Sri Aurobindo
 Along these lines, SA wrote –“Deprived of other weapons the nations are bound to have increasing resort to the weapon of commercial pressure. The corresponding weapons to lock-out would be the refusal of capital or machinery, the prohibition of all or of any needed imports into the offending or victim country, or even a naval blockade leading, if long maintained, to industrial ruin or to national starvation.” (From: “War and the Need of Economic Unity”, [Book_2, p 491) – Recent history is replete with examples of this – US & Cuba come to mind
 Paraphrased from “Pacifism and the Indian Spirit”, [Book_4, p 39 ]
 From the essay ”The Need of Military Unification”, [Book_2, p 478]
 From ”A First Step towards International Unity”, [Book_2, p 389]
 From the essay ”The Need of Military Unification”, [Book_2, p 484]
 From ”A First Step towards International Unity”, [Book_2, p 392]
 From the foreword, “War and Self-Determination”, [Book_2, p 601]
 From the essay “The Passing of War”, [Book_2, pp 610-611]