It was H.G. Wells who coined the phrase ‘the war that will end war’ and applied it to the conflict that broke out in the summer of 1914. It is now a bitterly ironic epithet for the First World War, which killed around 40 million people and was followed only two decades later by an even greater catastrophe. For a few years after the armistice in November 1918, however, it was an earnest and seemingly achievable ambition. Europe had, people hoped, been shocked into a fundamental change of mindset by the scale of the destruction. The way in which nations interacted had to change.

One hundred years ago, representatives of the United Kingdom, France, Germany, Belgium, Italy, Poland and Czechoslovakia met in the Swiss town of Locarno, on the northern shore of Lake Maggiore. Their common aim, although there were significant differences in approach, was to create a more sustainable peace than the one imposed by the Treaty of Versailles in 1919 and to guarantee as far as possible lasting peace on the continent of Europe. There was a genuine feeling that diplomacy could now succeed where previously countries had resorted to war – the Great War had shown that the cost in blood and treasure of armed conflict had spiralled beyond that which was endurable.

The Treaty of Versailles had dealt harshly with Germany. Arguably, Hungary suffered even more under the Treaty of Trianon, losing more than two thirds of its territory and population, but Germany was subject to punitive conditions: it lost 25,000 square miles of territory and seven million inhabitants; the output of the Saar coalfields would go to France for 15 years and the Saar Basin would be controlled by the League of Nations; the Rhineland was to be demilitarised.

Germany’s armed forces would be tightly limited to allow them only to serve as a defensive force. In addition, Germany was liable for reparations to the Allied Powers to the sum of 50 billion marks unconditionally, with additional amounts to be paid based on economic conditions, and, under Article 231, was required to accept responsibility for the war. All of this had not been subject to negotiations: the German delegation was presented with the terms as a fait accompli and instructed to sign.

Gustav Stresemann, Chancellor of Germany for a few months in 1923 but more significantly Minister of Foreign Affairs from 1923 to 1929, was a lower-middle-class economist and lawyer, who, before the First World War, had sat in the Reichstag for the National Liberal Party. In 1918 he founded the German People’s Party, a strange ideological pot pourri of patriotism, social conservatism, low taxation and small government, which prized the freedom of the individual from state interference above majoritarianism. He was marked by that same uneasy duality of strident nationalism and a liberal spirit.

Previously an avowed monarchist, Stresemann had come to terms with the institutions of the Weimar Republic. When Wilhelm Cuno’s minority administration resigned in August 1923 rather than face a vote of confidence in the Reichstag, which it was bound to lose, President Friedrich Ebert turned to Stresemann, who rapidly constructed a grand-but-shaky coalition of his German People’s Party, the Social Democrats, the Centre Party and the centrist German Democratic Party. Stresemann took the foreign ministry as well as the chancellorship, with the SPD’s Robert Schmidt as Vice-Chancellor and Minister for Reconstruction.

There was no formal coalition agreement; indeed, there was no policy platform at all. Stresemann, however, had a clear sense of what had to happen. The government had to stabilise the currency and rein in hyperinflation, then there was a series of steps towards restoring Germany to its rightful place as a sovereign nation: show willing in trying to meet the terms of the Versailles Treaty, use the goodwill of the Allies to speed up the withdrawal of French and Belgian occupying forces, find a compromise on the impossibly onerous reparations and gradually chip away at the strictures of the peace agreement.

Stresemann stepped down as Chancellor when the SPD withdrew its support and the government lost a confidence vote in November 1923, the Centre Party’s Wilhelm Marx replacing him, but he remained in the cabinet as Minister of Foreign Affairs – and would retain the post until his death in 1929. Suddenly, events seemed to run Germany’s way. A temporary currency, the Rentenmark, backed by a mortgage on land, began to curb the hyperinflation and the Currency Commissioner overseeing it, respected economist Hjalmar Schacht, was appointed President of the Reichsbank when the incumbent, Rudolf Havenstein, died unexpectedly of a heart attack.

After an approach by Stresemann, the Allies then set up a committee chaired by the former director of the US Bureau of the Budget, Brigadier General Charles E. Dawes, to re-examine Germany’s liabilities and economic capacity. The Dawes Plan, enacted in 1924, made a substantial step towards Stresemann’s long-term ambitions. It reduced reparations from 132 billion Reichsmarks to 50 billion, set out a staggered payment schedule, provided a loan of 800 million Reichsmarks to stabilise Germany’s economy and agreed the withdrawal of French and Belgian forces from the Ruhr.

Germany also benefited from a widening gap in policy between Britain and France. The overwhelming priority for France, invaded twice in 55 years, was security, and it had agreed alliances with Poland, Czechoslovakia, Romania and Yugoslavia to create a cordon sanitaire around Germany.

In November 1924, after the return of a Conservative government in London, 61-year-old former Tory leader Austen Chamberlain was appointed Foreign Secretary. The Prime Minister, Stanley Baldwin, notoriously easy-going, was not indifferent to foreign affairs, but he was content to entrust detailed policy to the much more experienced and senior Chamberlain.

This was good news for Germany and Stresemann’s strategic goals. Chamberlain saw a revitalised and normalised Germany as positive for European stability and encouraged a warmer relationship between Germany and France so that the latter would allow its cordon sanitaire in Eastern Europe to slacken. Once Poland, Czechoslovakia and the others realised their patron’s protection was not as reliable as they had hoped, they would, Chamberlain anticipated, gradually come to settlements with Germany over revisions of its eastern borders and ameliorate the most painful terms of Versailles.

At the beginning of 1925, Stresemann approached Britain and France secretly with a proposal: the three parties would sign a treaty committing to a peaceful resolution of disputes over the Rhineland, and Germany would guarantee the existing borders of France and Belgium, as well as committing to an arbitration pact with France. Chamberlain was cautious but receptive, as Stresemann’s plan fitted neatly with Britain’s existing policy, and French Foreign Minister Édouard Herriot and his successor Aristide Briand uneasily fell in line.

Rarely in politics do stars align exactly, but in 1925 it did seem as if there was an opportunity of a lasting diplomatic breakthrough. Britain, France and Germany all seemed broadly in agreement on a destination, and the two Allied countries were beginning to exhibit more optimism about the League of Nations. Still marked by the horrors and cost of the First World War, European leaders felt there was the possibility of a new chapter in international relations, what French historian Jean-Baptiste Duroselle drolly labelled ‘pactomania’.

Early September 1925 saw representatives of the UK, France, Germany, Belgium and Italy conduct initial meetings in London. Although Stresemann faced right-wing domestic opposition, and there were differences between Britain and France, the delegates sensed there was a deal to be done. At the suggestion of Belgian diplomat Henri Rolin, they agreed to reconvene in Locarno the following month to consider detailed terms.

The principal work was done between 5 and 16 October, with delegations led by Austen Chamberlain (UK), Aristide Briand (France), Gustav Stresemann and his Chancellor, Hans Luther (Germany), Emile Vandervelde (Belgium) and Senator Vittorio Scialoja (Italy). In addition, the foreign ministers of Czechoslovakia and Poland, Edvard Beneš and Aleksander Skrzyński, made their ways to Switzerland.

An astonishing amount was achieved in a short time. As well as the main treaty of mutual guarantee concluded by Germany, Belgium, France, the UK and Italy, Germany forged arbitration agreements – addenda to the principal document – with France and Belgium, and standalone arbitration treaties with Poland and Czechoslovakia. France also agreed new treaty arrangements with the two Eastern European countries.

All were initialled at Locarno on 16 October, Chamberlain’s 62nd birthday, and the normally staid Foreign Secretary sent a message to Sir William Tyrrell, his senior official, reading simply: ‘Cock-a-doodle-do!’

A formal signing ceremony took place on 1 December in the Italianate, Gilbert Scott-designed Reception Suite of the Foreign Office in London (now known as the Locarno Suite). Austen Chamberlain, newly created a Knight of the Garter, presided over a day of great ceremony and gravitas, while his French counterpart, Briand, waxed lyrical:

‘The spirit of Locarno which is consecrated in these treaties means coming cooperation among the European nations; it means a common effort by those who confronted each other in the World War now to restore the old Continent to solidity and tranquility.’

Locarno could have changed Europe. The treaty of mutual guarantee made inviolable the German frontiers with Belgium and France, as set out in the Treaty of Versailles, and confirmed the demilitarisation of the Rhineland; the three nations also committed to resolve any future disputes through the League of Nations, which Germany would join in September 1926. The arbitration agreements reinforced this by creating Permanent Conciliation Commissions to manage any disputes in the first instance.

Germany’s treaties with Czechoslovakia and Poland were broadly similar but non-binding. However, the latter countries were by separate treaty guaranteed assistance from France if either was attacked.

There were weaknesses and lacunae, and Stresemann certainly did not intend Locarno to be a final settlement of Germany’s eastern borders. But Czechoslovakia had only been created in 1918 from the wreckage of the Habsburg Empire, while the Second Polish Republic was established the same year, 123 years after an independent Poland had vanished from the map under the Third Partition of 1795. These were new, uncertain borders and future adjustments did not have to mean huge territorial losses or annihilation, though the dark fears of the Polish political class would eventually be exceeded.

On the other hand, as 1926 dawned, Western Europe seemed at peace under a kind of Versailles 2.0. Germany had abandoned her claims on Alsace and Lorraine, and the demilitarised Rhineland was a reassuring buffer, notwithstanding that the French and Belgian borders were underwritten by treaty. Stability and Germany’s impending admission to the League of Nations allowed Stresemann, under three successive chancellors, to concentrate on economic growth and closer ties with the United States.

In December 1926, the Norwegian Nobel Committee announced that the Peace Prize for 1925, which had not been awarded, would be given to Austen Chamberlain ‘for his crucial role in bringing about the Locarno Treaty’ and US Vice President Charles Dawes for his work on German reparations. The 1926 prize was awarded to Aristide Briand and Gustav Stresemann, also in recognition of Locarno.

For a few years, international politics augured well. The Dawes Plan had made the payment of reparations manageable, as Germany enjoyed its Goldene Zwanziger, the Golden Twenties; the Allied occupation forces gradually evacuated the Rhineland; the Franco-American Kellogg-Briand Pact of 1928 saw signatories disavow war to resolve disputes; 1929’s Young Plan set out a final schedule for reparations which would end in 1988 after the payment of 112 billion Reichsmarks; and France withdrew from the Rhineland in 1930, five years ahead of schedule.

But it was not to be. As Harold Nicolson, then a British diplomat, later wrote, ‘the Heavenly alchemy of the Locarno spirit, the triumphant splendour of those autumn days, did not prove of long endurance’. Chamberlain left office with the Conservative government in June 1929, Stresemann died after a series of strokes in October and Germany’s Weimar Republic slid towards chaos and the rise of Nazism. Three weeks after Stresemann’s death came the Wall Street Crash, and the Great Depression would follow in its wake.

One hundred years on, the Locarno Treaties seem stereotypical of the 1920s: eager, breathless, lacquered with a brittle, innocent optimism. Mankind knew, surely, that it could never afford to revisit the carnage and brutality of the Great War and its 40 million dead. Memorials in towns and villages everywhere spoke eloquently of that. None of the players, not Stresemann, nor Chamberlain, nor Briand, Dawes or Kellogg could have contemplated a bloodier conflict. Only Dawes would live to see it; perhaps he was the unlucky one.