Since September 18, the eyes of the rugby-following world have been firmly focused on England, where the Rugby World Cup is being played. It is appropriate that the eighth quadrennial competition takes place in 2015, a year in which almost all the countries participating in this epic sporting event are also marking the centenary of World War I. The relationship between rugby and war has been intertwined since the game’s founding, when an English schoolboy caught and ran with a football in his arms during a football (or soccer, as American readers will insist) game at Rugby School in 1823.

William Webb Ellis, the schoolboy after whom the Rugby World Cup trophy is named, was only attending Rugby School after his father, an officer in the Dragoon Guards, was killed at the Battle of Albuera in 1811. His death left his family to survive on a small army pension that forced his surviving wife and children to move to Rugby, where schooling was free.

Beyond the story of the sport’s founding, the relationship between rugby and war is perhaps most evident in the case of New Zealand. The performance of New Zealand forces during WWI — initially at Gallipoli and later on the Western Front and in the Middle East — was an important part of New Zealand’s identification as an independent state, rather than merely a part of the British Empire. As an independent nation, both New Zealand’s military deployments and its rugby success would shape the perception of the country abroad and its internal national identity.

The national rugby team of New Zealand, the All Blacks, was touring Australia in 1914 when war was declared. As they sailed home, the entire team made a pact that they would volunteer upon their arrival. Of the 50 All Blacks who served in World War One, 13 did not return. Those 13 who perished were among the more than 115 internationally capped rugby players who would be killed fighting for the Allied forces in the war. Lieutenant Frank Gard of the U.S. Army, who was killed near the Meuse River in 1918, had captained the U.S. side against the All Blacks in California in 1913. The most notable New Zealand player to be killed was Sergeant Dave Gallaher, who had fought in the Second Boer War before leading the Original All Blacks of 1905. Despite Gallaher’s exemption from conscription due to his age, he volunteered again to serve in WWI and was subsequently killed at the Battle of Passchendaele in 1917 at the age of 43.

The New Zealand Division’s rugby team played seven matches during the 1916-1917 season in Europe, scoring 292 points and allowing only nine to be scored against them. The highlight of this tour was a 40–0 victory over the French team in front of a crowd of 60,000 Parisians. Though the use of the haka had started ten years earlier, the 1916–1917 European tour saw the first written reference to the traditional war dance, perhaps the most obvious example of the link between rugby and New Zealand’s warrior tradition. In 1919, after the war finished, a New Zealand Army team toured Great Britain, France and South Africa.

That the same skillsets and qualities that define a good rugby player also define a good soldier is not a new or startling observation.

The British General Staff identified sports as a key part of platoon training, issuing supportive training guidance in 1918: “too much attention cannot be paid to the part played by games in fostering the fighting spirit.” Along with boxing, rugby was identified by the British armed forces as an activity that “promoted tough masculinity.” The links continue to this day as national rugby teams train with military units as part of their preparations for international test matches. For instance, the U.S. Eagles spent several days training at a Royal Navy facility as part of their preparation for the current Rugby World Cup, while the referees underwent a three-day team-building exercise with the British Royal Marines.

In New Zealand, studies of the Kiwi identity clearly link rugby and war, with one stating that “rugby was seen as either a substitute or preparation for war.” All Black player Thomas Ellison said in 1902 that rugby was “a soldier-making game.” Yet the relationship between rugby and war works in both directions. David Gallaher’s leadership of the 1905 All Blacks has been attributed to qualities he gained from his military experience in South Africa: “discipline, cohesion and steadiness under pressure.”

The unique connection between rugby and the military established so long ago continues today. Each year, for instance, the British Army and Royal Navy rugby unions play the annual Army Navy Match, as they have done since 1909 — interrupted only by World Wars I and II. And they do so in front of 80,000 fans. At the same time as the Rugby World Cup of 2015 is being played, the International Defence Rugby Competition is also being held in England, during which ten rugby teams from defense forces around the world will vie for international supremacy in a parallel tournament to their civilian counterparts.

Around 1900, rugby was said to be “the best trial of the relative vigour and virility of any two or more opposing countries.” These six weeks in England will be no exception.

Ruben Stewart is a retired New Zealand infantry officer and rugby fan who most recently played for the Jerusalem Lions. After more than ten years of active service he has since served as an advisor to NATO and a consultant to the U.S., U.K. and other allied militaries and governments, international organizations and NGOs.