There are two things to consider here. One is the book, compiled out of eleven newspaper and magazine articles Wells published in the first months of the First World War. The other is the title itself. Because where the book is an object lesson in what happens to hostages-to-fortune under the withering glare of hindsight, the title may be one of the most famous phrases ever to come from Wells's pen.
So to start with the first of these two things, the book itself. It has not, I'm afraid, aged well.
Chapter I. Why Britain Went to WarWells blames the war entirely on German aggression, and more specifically on Prussian militarism (it's possible, just possible, that the actual causes of the war were a little more complex than that). He is certain that Germany will lose, and soon (that within ‘two or three months’ the entire edifice of ‘German Imperialism will be shattered’): that ‘Prussianism took its mortal wound at the first onset before the trenches of Liege. We begin a new period of history’; that ‘the German repulse at Liege was but the beginning of a German disaster as great as that of France in 1871’; and that
Chapter II. The Sword of Peace
Chapter III. Hands Off the People's Food
Chapter IV. Concerning Mr. Maximilian Craft
Chapter V. The Most Necessary Measures in the World
Chapter VI. The Need of a New Map of Europe
Chapter VII. The Opportunity of Liberalism
Chapter VIII. The Liberal Fear of Russia
Chapter IX. An Appeal to the American People
Chapter X. Common Sense and the Balkan States
Chapter XI. The War of the Mind
if you want to see where diplomacy and Weltpolitik have landed Europe after forty years of anxiety and armament, you must go and look into the ditches of Liege. These bloody heaps are the mere first samples of the harvest. [War That Will End War, 6]Nor was he alone in thinking that the defence of Liège constituted a war-ending repulse to the Germans. Here's a contemporaneous Punch cartoon:
In fact Liège fell relatively quickly, on the 16th August 1914, and the defence it mounted delayed the German advance by a couple of days at most (plus: it cost as many as 20,000 Belgian lives, as against 5000 German casualties). So the gate in that cartoon very speedily had the ‘No’ before its ‘Thoroughfare’ erased.
Since Wells is certain the Germans are in the process of being defeated, he gives a lot of time to the question of how to order the postwar world. For example, he proposes completely redrawing the map of Europe (‘I suggest that France must recover Lorraine, and that Luxemburg must be linked in closer union with Belgium. Alsace, it seems to me, should be given a choice between France and an entry into the Swiss Confederation .. the break-up of the Austrian Empire has hung over Europe like a curse for forty years. Let us break it up now and have done with it ... then, I would suggest that the three fragments of Poland should be reunited, and that the Tsar of Russia should be crowned King of Poland’ and so on, for many pages). As far as this goes, he is at least cheerily up-front about his complete lack of expertise—‘I am a fairly ignorant person ... and I admit a certain sense of presumptuous absurdity as I sit here before the map of Europe like a carver before a duck and take off a slice here and decide on a cut there’—although he does nonetheless insist upon its urgent needfulness. Once again, hindsight is not on Wells's side where this kind of thing is concerned (there are plenty of examples of the damage it can do).
More worryingly still, the book contains a deal of raw, anti-Semitic blather:
In the South and East [of the Russian empire] are certain provinces thick with Jews, whom Russia can neither contrive to tolerate nor assimilate, who have no comprehensible projects for the help or reorganisation of the country, and who deafen all the rest of Europe with their bitter, unhelpful tale of grievances, so that it is difficult to realise how local and partial are their wrongs. [War That Will End War, 1]‘Thick with Jews’ is an especially unpleasant piece of phraseology, isn't it? It's not that Wells is unaware of the series of anti-Jewish pogroms conducted in Russia between 1881 and the years in which he was writing. It's that, in his own words, Jewish prominence ‘in the English and still more in the American Press’ has had the effect of ‘distort[ing] the issue of this’, an argument with some very alarming implications. He also asserts that ‘the Jews by their particularism invite the resentment of all uncultivated humanity.’ Invite it, no less!
Anyhow: Wells proposes a Balkan League to solve the Balkan Problem (indeed he asserts, breezily, that ‘the Balkan States never have been a problem’), and presses hard on the need for Propaganda:
By means of a propaganda of books, newspaper articles, leaflets, tracts in English, French, German, Dutch, Swedish, Norwegian, Italian, Chinese and Japanese we have to spread this idea, repeat this idea, and impose upon this war the idea that this war must end war. We have to create a wide common conception of a re-mapped and pacified Europe, released from the abominable dangers of a private trade in armaments, largely disarmed and pledged to mutual protection. [War That Will End War, 8]That passage comes near the end of the book, and contains the main text's only iteration of the titular slogan.
Which brings me to that slogan. I'd say that there are three phrases in particular, out of all the many phrases and ideas Wells coined, that have enjoyed the most widespread and enduring afterlife: time machine, atom bomb and the war to end war. This latter has a particularly pungency, since it went in short order from being heartfelt and genuine rallying cry to an ironic, bitter, reflection on a conflict that killed seventeen million, maimed twenty million more and ruined a continent without resulting in larger benefit for humankind of any kind. Wells here uses the phrase ingenuously; when he cites it again in his later novel The Bulpington of Blup he does so with rather sour irony. You see, it turns out that—spoiler—this war didn't actually end war after all.
And The War That Will End War is a frankly self-contradictory title:—one might as well call a book The Cholera Bacillus That Will End Dysentery or Fucking for Virginity. Hindsight, to put it bluntly, licences us to mock Wells (and several of his prophecies really do look rather naïve: that it will become globally illegal to produce warships, for instance, and the oceans of the world free of armied navies ‘for hundreds of years’). His larger twofold point is not so far-fetched, I suppose: that militarism can only be defeated militarily, and that a victory so won will give the world the chance at collective disarmament, ‘at a settlement that shall stop this sort of thing for ever.’ Even so:
Every soldier who fights against Germany now is a crusader against war. This, the greatest of all wars, is not just another war—it is the last war! [War That Will End War, 1]Say what you like about the crusades, they at least put an end to all religiously-grounded conflict and war forever.
I shouldn't be sarcastic. It's no laughing matter. And yet the phrase continues to endure. Of the various versions of it, ‘The War To End War’ (or the ‘War To End All War’), ‘This War Must End War’ ‘Making War on War’ and so on, I think Wells's title here is the best: something to do with the way it follows its initial iamb with two unstressed and then two stressed syllables—technically this latter is called a minor ionic, or sometimes a double iamb—which is prosodically quite forceful.