Great Warと大文字ならば

上記のPBSドキュメンタリーはThe Great War and The Shaping of the 20th Centuryという題名で、第一次世界大戦を扱っています。

このあたりはロングマンにも載っています。Great Warは昔の呼び名のようです。World War Iではfor British people the strongest image is of the 'Western Front' in Belgium and northern France, where the armies of each side lived in trenches (=long deep holes in the ground), with an area called "no-man's land" between them.と英国人のイメージも説明してくれて丁寧ですね。こういうのは外国人にとってはありがたいです。

（ロングマン）
Great War, the
an old-fashioned name for World War I

World War I also the First World War
(1914-1918) a war in Europe fought between France, the UK and its empire, Russia, and the US on one side ('the Allies'), and Germany, Austria-Hungary, and Turkey on the other side. The war started as a result of the murder in Sarajevo of the Archduke Franz Ferdinand, a member of the Austrian royal family. World War I was fought in many different areas, but for British people the strongest image is of the 'Western Front' in Belgium and northern France, where the armies of each side lived in trenches (=long deep holes in the ground), with an area called "no-man's land" between them. Many of the famous battles on the Western Front ended without either side gaining much land, and the names of these battles especially the Somme, Passchendaele, and Ypres, have come to represent the way that millions of young men were killed for no very good reason. For people from Australia and New Zealand, the battle of Gallipoli, where thousands of their soldiers were killed, is remembered with great sadness.

第一次世界大戦の呼び名については、Wikipediaが以下のように説明してくれています。当時はWorld WarとかGreat Warとか呼ばれていたようですね。

（Wikipedia）
Names
From the time of its occurrence until the approach of World War II, it was called simply the World War or the Great War and thereafter the First World War or World War I.[14][15]

In Canada, Maclean's Magazine in October 1914 said, "Some wars name themselves. This is the Great War."[16] During the Interwar period (1918-1939), the war was most often called the World War and the Great War in English-speaking countries.

The term "First World War" was first used in September 1914 by the German philosopher Ernst Haeckel, who claimed that "there is no doubt that the course and character of the feared 'European War' ... will become the first world war in the full sense of the word."[17] After the onset of the Second World War in 1939, the terms World War I or the First World War became standard, with British and Canadian historians favouring the First World War, and Americans World War I.


下記の説明では、アメリカでは参戦するまではEuropean Warで、アメリカが参戦するとWorld Warになったとあります。

MARCH 6, 2013
Were they always called World War I and World War II?
The short answer is no, though it’s hard to pinpoint precisely when the World War I and World War II—or First World War and Second World War—monikers arose. During World War I, of course, nobody knew that a second global conflict would follow closely on the heels of the first, so there was no need to distinguish it as the first of its kind. After initially referring to the “European War,” U.S. newspapers adopted “World War” once America entered the confrontation in 1917. On the other side of the Atlantic, meanwhile, Britons preferred “Great War” until the 1940s—with the notable exception of Winston Churchill, who reminisced about the “World War” in the 1927 volume of his memoir “The World Crisis.”

BBCは一次大戦の特設サイトを作っていますが、下記の記事では19世紀以前にも「世界大戦」と呼びうるものがあったのではという問題意識で始まっています。

28 June 2014 Last updated at 23:45
WW1: Was it really the first world war?
By Heather Jones
London School of Economics

After 1945, historians found the term "First World War" appropriate because they saw 1914-1918 as the first of a particular type of international conflict - the world's first industrialised "total" war - which had been followed by a second industrialised world war of this kind - 1939-1945.

There are certainly arguments that can be made, however, that the titles "First World War" and "World War One" are misleading. The Seven Years War, the mid-18th Century battle for supremacy among Europe's great powers, and the Napoleonic Wars were also fought across the globe, on multiple continents causing severe disruption to global trade. Moreover, if measured in comparison to World War Two, which saw widespread fighting in China, South-East Asia and the Pacific, then 1914-1918 looks more like a European conflict - the key fronts that would decide the outcome of the war were all in Europe.

18世紀の７年戦争や19世紀のナポレオン戦争と比較しながら、世界的な影響の大きさを考えると、やっぱりFirst World Warが最初の世界大戦だと常識的な結論に落ち着いています。

If we measure the war in terms of its ideological effects it was clearly global. The war's economic legacy changed the world as the capital of finance shifted during the conflict from London to New York and, with vast swathes of European agriculture ruined, Argentina and Canada greatly increased their market share as food suppliers.

Global attitudes were also changed. The Japanese called for a clause on the equality of all races to be inserted into the League of Nations covenant after the war - they were unsuccessful, but the idea revealed changing mindsets. The first Pan-African Congress, held in Paris in 1919, advocated that African peoples should govern themselves. The war's legacy was new global ideas about the right of peoples to self-determination and the need for a global system of international co-operation, which was embodied in the League of Nations.

It was a war that utterly altered the world and in this regard, in the sheer scale of the changes it brought, it was certainly a first.

冒頭に紹介したPBSのドキュメンタリーシリーズを以下にメモ代わりに置いておきます。