First World War? That was probably the most pointless war in history... I mean really? A Bosnian-Serb nationalist kills the Archduke Franz Ferdinand of Austria, so lets all fight Germany and the Central Powers! Plus, WWI wasn't even much of a world war, look at these two maps of participants in WWI and WWII
(for the first image, most of Africa were still colonies of Europe, so those couldn't be counted towards it being most of the world at war, just more European powers)
I feel it was pretty pointless in hindsight as well, or maybe the right words are: more unnecessary, avoidable and wasteful than most wars. But the topic is still of interest to us, maybe for these reasons, as all history is of potential interest to us. Regarding the range of the conflict, certainly the vast majority of it was confined to Europe. They never called it WWI until WWII, (fancy that

) it was simply known as the Great War, supposedly to end all wars. But the degree of participation was still widespread globally, and Dachs already made the point about colonial empires. They were caught up in it as well.
There were engagements worldwide, but to complete the comparison with WWII, it was pretty limited, obviously since Japan was our ally in this one. There is the Middle East campaign in Palestine, the Levant, and Mesopotamia of course, which compares to that of North Africa in WWII, and the Caucasus front, but Gallipoli on the European side was a bigger operation than both of those. The Tanganyika campaign is very notable because at one time it tied down about 6 allied divisions, but other than that there was only a brief resistance in SW Africa (Namibia) and Tsingtao in the far east. Likewise the naval campaign; von Spee's small cruiser squadron had some success in the Pacific before being annihilated at the Falklands. Only the dramatic escape and depredations of the
Emden, and a couple of low rate merchant raiders, continued for awhile. Even the submarine war was mostly confined to the western approaches of Europe.
Actually the Seven Years War was the first real world war, with major actions in North America, the Caribbean, India, and even a few places in Africa and the Pacific Rim. Ditto for the American Revolution, though it was confined in Europe to naval engagements or joint operations like Gibraltar. Much more so the Napoleonic Wars; add South America and the Middle East, and you could include the War of 1812.
I think there is a different kind of emphasis when we say WWI was 'pointless', or unnecessary. As Dachs succinctly stated, there are many pertinent reasons it escalated. Europe was a powder keg ready to blow, something probably would have happened sooner or later anyway. I can only speak to what did happen, but the points I want to make are on a different level.
The outcome of these alliances and cross-ultimatums was far out of proportion to the original
cassus belli . There was no act of aggression by a major power. It lacked the just cause for the nations of Europe to engage in a dust-up, just like the pre-nationalism alliance wars of previous centuries. With a taste of what war would be like in the modern age starting at Crimea, Solferino, Sadowa and others, one would think a minimum of diplomatic effort could have kept this to a regional dispute with both Russia and Austria-Hungary able to protect their interests, and other parties arbitrating. But Germany was ambitious, and France was spoiling for another round in the Franco-Prussian War, as long as there were some powerful allies to back her. Whatever the reasons, the nations cheerfully mobilized for what they thought would be a short, decisive war; and their leaders failed them again by inadequately anticipating what they were getting in to. As a percentage of those engaged, WWI by far exceeded the casualty rates suffered by the participants of WWII. Even the percentages of Russia and Germany were at least comparable, (not counting Japan - since its involvement in WWI was little more than a police action by comparison). The total death and disabled toll to Britain and its Commonwealth allies was three times as high, and to France there is no comparison. The territory that changed hands, was again completely disproportionate to the cost; a band of mud-soaked fields 30-50 miles in depth on the western front, and mostly marsh and woodland along the borders of the eastern front, before the Russian collapse. What did it gain ? The realignment of Germany's borders to pre-Bismarck days, the collapse of the old orders, and fragmentation of the empires into new states. In its wake came the 'Spanish' influenza epidemic, the Bolshevik revolution, and the rise of Fascism. Making it for me, the most lethal, and futile, conflict in history. Remembrance Day (Veteran's Day in the US) marks its end, but I think the original meaning was lost. No wonder the writers of the day coined the term the 'Lost Generation'.

In 20 years the western democracies would fail to prevent an even bigger war. But this time there was little of the disillusionment and demoralization of WWI, except for the Axis once they started losing badly.
Sorry for getting on the soap box and saying what you all doubtless already know, but I just had to add my own perspective. There aren't many good films on WWI, but of course there is the story told from a German soldiers point of view
All Quiet on the Western Front Both the original and the remake with Richard Thomas and Ernest Borgnine are highly recommended, along with Kubrick's
Paths of Glory. Even the modest budget Canadian production
Passchendaele is worth seeing, that 'miracle' really happened apparently.