There is no doubt that all nations are aggressive; it is the nature of man. There start up from time to time between countries antagonistic passions and questions of conflicting interest, which, if not properly dealt with, would terminate in the explosion of war. Now, if one country is led to think that another country, with which such questions might arise, is from fear disposed on every occasion tamely to submit to any amount of indignity, that is an encouragement to hostile conduct and to extreme proceedings which lead to conflict. It may be depended on that there is no better security for peace between nations than the conviction that each must respect the other, that each is capable of defending itself, and that no insult or injury committed by the one against the other would pass unresented.

Wars are motivated by the need to seize the wealth of our neighbours, to wield power, to protect ourselves from real or imagined threats: in short they have, as we have seen, political, social, economic or demographic causes. There is no need to refer to Islam or the clash of civilizations to explain why the Afghans or the Iraqis resist the western military forces occupying their countries. Nor to speak of anti-Jewish sentiment or anti-Semitism to understand the reasons why the Palestinians are not overjoyed by the Israeli occupation of their lands.

Born enemies don't fight. Nations you would say were designed to go to war against each other — by their skins, their language, their smell: always jealous of each other, always hating each other — they're not the ones who fight. You will find the real antagonists in nations fate has groomed and made ready for the same war.

The Nation, which indulges towards another an habitual hatred, or an habitual fondness, is in some degree a slave. It is a slave to its animosity or to its affection, either of which is sufficient to lead it astray from its duty and its interest. ... The Nation, prompted by ill-will and resentment, sometimes impels to war the Government, contrary to the best calculations of policy. The Government sometimes participates in the national propensity, and adopts through passion what reason would reject; at other times, it makes the animosity of the nation subservient to projects of hostility instigated by pride, ambition, and other sinister and pernicious motives. The peace often, sometimes perhaps the liberty, of Nations has been the victim.

It is too true, however disgraceful it may be to human nature, that nations in general will make war whenever they have a prospect of getting anything by it; nay, absolute monarchs will often make war when their nations are to get nothing by it, but for the purposes and objects merely personal, such as thirst for military glory, revenge for personal affronts, ambition, or private compacts to aggrandize or support their particular families or partisans. These and a variety of other motives, which affect only the mind of the sovereign, often lead him to engage in wars not sanctified by justice or the voice and interests of his people.

In all history there is no war which was not hatched by the governments, the governments alone, independent of the interests of the people, to whom war is always pernicious even when successful. The government assures the people that they are in danger from the invasion of another nation, or from foes in their midst, and that the only way to escape this danger is by the slavish obedience of the people to their government. This fact is seen most prominently during revolutions and dictatorships, but it exists always and everywhere that the power of the government exists. Every government explains its existence, and justifies its deeds of violence, by the argument that if it did not exist the condition of things would be very much worse. After assuring the people of its danger the government subordinates it to control, and when in this condition compels it to attack some other nation. And thus the assurance of the government is corroborated in the eyes of the people, as to the danger of attack from other nations.

[G]overnments always need enemies, even when they're not at war. If you don't have a real enemy, you make one up and spread the word. It scares the population, and when the people are scared, they tend not to step out of line.

Wars happen because the ones who start them think they can win.

Scholars know where civil wars break out and who tends to start them: downgraded groups in anocracies dominated by ethnic factions. But what triggers them? What finally tips a country into conflict? Citizens can absorb a lot of pain. They will accept years of discrimination and poverty and remain quiet, enduring the ache of slow decline. What they can’t take is the loss of hope. It’s when a group looks into the future and sees nothing but additional pain that they start to see violence as their only path to progress.

People fear/hate other nations only when they don't know them.

Although it is commonly supposed that war making is the specific activity of nations, the blind rage that motivates war destroys the very social bonds that make nations possible. Of course, it can fortify the nationalism of a nation, producing a provisional coherence bolstered by war and enmity, but it also erodes the social relations that make politics possible. The power of destruction unleashed by war breaks social ties and produces anger, revenge, and distrust (“embitterment”) such that it becomes unclear whether reparation is possible, undermining not only those relations that may have been built in the past, but also the future possibility of peaceful coexistence.

Preparedness to use the weapons of war creates the tempers, the quarrels and the crises which lead to the outbreak of war.

If every nation is going to be our rival, if every nation is going to dislike and distrust us, and that will be the case, because having trusted us beyond measure the reaction will occur beyond measure (as it stands now they trust us they look to us, they long that we shall undertake anything for their assistance rather than that any other nation should undertake it)— if we say, "No, we are in this world to live by ourselves, and get what we can out of it by any selfish processes," then the reaction will change the whole heart and attitude of the world toward this great, free, justice-loving people, and after you have changed the attitude of the world, what have you produced? Peace? Why, my fellow citizens, is there any man here or any woman, let me say is there any child here, who does not know that the seed of war in the modern world is industrial and commercial rivalry? The real reason that the war that we have just finished took place was that Germany was afraid her commercial rivals were going to get the better of her, and' the reason why some nations went into the war against Germany was that they thought Germany would get the commercial advantage of them. The seed of the jealousy, the seed of the deep-seated hatred was hot, successful commercial and industrial rivalry.

But our energies are directed far more toward war. Hypnotized by mutual mistrust, almost never concerned for the species or the planet, the nations prepare for death. And because what we are doing is so horrifying, we tend not to think of it much. But what we do not consider we are unlikely to put right.
Every thinking person fears nuclear war, and every technological state plans for it. Everyone knows it is madness, and every nation has an excuse.