World War I
Technology: World War I began as a clash of 20th-century technology and 19th-century tactics, with the inevitably large ensuing casualties. By the end of 1917, however, the major armies had modernised and were making use of telephone, wireless communication, armoured cars, tanks (especially with the advent of the prototype tank, Little Willie), and aircraft.

Artillery also underwent a revolution. In 1914, cannons were positioned in the front line and fired directly at their targets. By 1917, indirect fire with guns (as well as mortars and even machine guns) was commonplace, using new techniques for spotting and ranging, notably, aircraft and the field telephone.
Fixed-wing aircraft were initially used for reconnaissance and ground attack. To shoot down enemy planes, anti-aircraft guns and fighter aircraft were developed. Strategic bombers were created, principally by the Germans and British, though the former used Zeppelins as well. Towards the end of the conflict, aircraft carriers were used for the first time, with HMS Furious launching Sopwith Camels in a raid to destroy the Zeppelin hangars at Tønder in 1918.

Diplomacy: The non-military diplomatic and propaganda interactions among the nations were designed to build support for the cause or to undermine support for the enemy. For the most part, wartime diplomacy focused on five issues: propaganda campaigns; defining and redefining the war goals, which became harsher as the war went on; luring neutral nations (Italy, Ottoman Empire, Bulgaria, Romania) into the coalition by offering slices of enemy territory; and encouragement by the Allies of nationalistic minority movements inside the Central Powers, especially among Czechs, Poles, and Arabs. In addition, multiple peace proposals were coming from neutrals, or one side or the other; none of them progressed very far.

Legacy and memory: 

Memorials: Memorials were built in thousands of villages and towns. Close to battlefields, those buried in improvised burial grounds were gradually moved to formal graveyards under the care of organisations such as the Commonwealth War Graves Commission, the American Battle Monuments Commission, the German War Graves Commission, and Le Souvenir français. Many of these graveyards also have monuments to the missing or unidentified dead, such as the Menin Gate Memorial to the Missing and the Thiepval Memorial to the Missing of the Somme.
In 1915, John McCrae, a Canadian army doctor, wrote the poem In Flanders Fields as a salute to those who perished in the war. It is still recited today, especially on Remembrance Day and Memorial Day.

National World War I Museum and Memorial in Kansas City, Missouri, is a memorial dedicated to all Americans who served in World War I. The Liberty Memorial was dedicated on 1 November 1921.
The British government budgeted substantial resources to the commemoration of the war during the period 2014 to 2018. The lead body is the Imperial War Museum. On 3 August 2014, French President François Hollande and German President Joachim Gauck together marked the centenary of Germany's declaration of war on France by laying the first stone of a memorial in Vieil Armand, known in German as Hartmannswillerkopf, for French and German soldiers killed in the war. As part of commemorations for the centenary of the 1918 Armistice, French President Emmanuel Macron and German Chancellor Angela Merkel visited the site of the signing of the Armistice of Compiègne and unveiled a plaque to reconciliation.

Historiography: The first efforts to comprehend the meaning and consequences of modern warfare began during the initial phases of the war and are still underway more than a century later. Teaching World War I has presented special challenges. When compared with World War II, the First World War is often thought to be "a wrong war fought for the wrong reasons"; it lacks the metanarrative of good versus evil that characterizes retellings of the Second World War. Lacking recognizable heroes and villains, it is often taught thematically, invoking simplified tropes that obscure the complexity of the conflict.
Historian Heather Jones argues that the historiography has been reinvigorated by a cultural turn in the 21st century. Scholars have raised entirely new questions regarding military occupation, radicalisation of politics, race, medical science, gender and mental health. Among the major subjects that historians have long debated regarding the war include: Why the war began; why the Allies won; whether generals were responsible for high casualty rates; how soldiers endured the poor conditions of trench warfare; and to what extent the civilian home front accepted and endorsed the war effort.

Unexploded ordnance: As late as 2007, unexploded ordnance at battlefield sites like Verdun and Somme continued to pose a danger. In France and Belgium, locals who discover caches of unexploded munitions are assisted by weapons disposal units. In some places, plant life has still not recovered from the effects of the war.

See also: Lists of World War I topics
List of military engagements of World War I
Outline of World War I
World war
World War II

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External links: Links to other WWI Sites, worldwide links from Brigham Young U.
The World War One Document Archive, from Brigham Young U.
International Encyclopedia of the First World War
Records on the outbreak of World War I from the UK Parliamentary Collections
The Heritage of the Great War / First World War. Graphic colour photos, pictures and music
A multimedia history of World War I
European Newspapers from the start of the First World War and the end of the war
WWI Films on the European Film Gateway
The British Pathé WW1 Film Archive Archived 24 March 2019 at the Wayback Machine
World War I British press photograph collection – A sampling of images distributed by the British government during the war to diplomats overseas, from the UBC Library Digital Collections
Personal accounts of American World War I veterans, Veterans History Project, Library of Congress
Who is at fault for World War I? (YouTube Premium): Link

Library guides: National Library of New Zealand
State Library of New South Wales
US Library of Congress
Indiana University Bloomington Archived 5 June 2015 at the Wayback Machine
New York University Archived 5 April 2015 at the Wayback Machine
University of Alberta
California State Library, California History Room. Collection: California. State Council of Defense. California War History Committee. Records of Californians who served in World War I, 1918–1922.