I've always wondered what defines a world war as opposed to a normal war, is there a specific guideline for this or was it just decided when naming the war?
I've talked about this quite extensively so I'll just copy paste my reply the last time this question was posted:
The reason we call them the First World War and the Second World War is because that's what people at the time called them and it's what they've been called for going on a hundred years now. Obviously they weren't the first war that took place across 2+ continents or to involve two powers on 2+ modern defined continents but that's not the point: That's what people called them, it's what they've been called for decades, that's what they're called -- first by the German Ernst Haeckel in September 1914 and again by Charles à Court Repington in 1920. There is no international organization or cabal of historians 'naming' things -- it's just we call it what people call it and things stick. That's the true reason, honestly.
The 'more logical' reason, what we can use to justify this position retrospectively, and perhaps the most common modern justification, is that those wars were European wars which just extended to their colonies which happened to be overseas. They weren't 'global' conflicts in that respect they were localized conflicts with localized goals which just had extended fighting -- every single war you listed fits that bill. Outside of the Mughal Empire in the 7 Years' War they're all European powers. The First World War was the first truly global war which hit every single continent. Japan and China and East Pacific colonies, India, Australia, South, East, North, and West Africa, Eastern Europe, Western Europe, the North Sea, Brazil, Central America, North America. Every single corner of the Earth, all from independent or quasi-independent dominions (Australia, Canada, South Africa, New Zealand) operated as independent military entities and as independent government actors. That had never been done before, ever.
Yes we have the 7 Years' War but it was what, a few European colonies which saw next to no fighting in Africa, some small conflicts in coastal India, and Russia who were fighting just about entirely in Europe anyways? Everywhere you extend outside of 'Europe' are European powers and European armies fighting other Europeans with the small exception of in North America where Indians admittedly played a larger role. It was still, ultimately, a war between Prussia/Great Britain/Central German States/Portugal vs France/Austria/Russia/Spain/Saxony/Mughal Empire...with the latter being the non-European entity obviously.
Other common cited examples are like the 80 Years' War (which bled into the 30 Years' War...but the Eighty Years' War was a war concerning Dutch independence. Some people jumped in and out and it was involved in for instance the 30 Years' War and some fighting took place outside of the Netherlands but the fact is it was a war between the United Provinces & Friends vs Spain & Friends for Dutch independence. That was the goal. It was a war between England, United Provinces, France, the Holy Roman Empire, and Spain -- that's not a 'world war'.
All other examples follow the same pattern: Nine Years' War was basically a religious war and expansionism from Louis w.r.t. Europe that had some light fighting in North American colonies. Spanish Succession War was literally just fighting over the Spanish crown, and the Austrian succession war similarly. These are European conflicts between European powers for European goals and when they do extend globally in some fashion it's so extremely limited it hardly deserves the denoting of 'world war'.
Think of it like this: You wouldn't call the Gulf War World War 3 even though it was the U.S. & Friends (America & Europe) vs Iraq (Asia), would you? It had global participants, significant casualties, etc. It's the same thing here honestly: None of these commonly listed wars linked involved the popular participation of everyone everywhere even though they, at times, involved some powers from not-Europe and fighting in not-Europe. A 'world war' is not just who is fighting or where but scale and affect. No one was unaffected by WW1 or WW2. Yes it was started in Europe but its participants not only went beyond Europe those directly and largely affected were as well. 1.5 million Indians would volunteer to fight, America drafted nearly 3 million people, 40% of the Australian male population would enlist, fighting would occur off the coast of Brazil and just about all of Central and South America would come on the side of the Allies as independent, sovereign states. China would send tens of thousands of men to contribute to trench building and also providing supplies while Japan seized numerous German colonies in the Pacific in blatant expansionism. Africa was a theater of independent, quasi-independent, and European fighting forces that raged throughout the war.
Numerous, global belligerents had numerous goals (America expanding trade power in the post-war world, basically any laundry list of European reasons, Ottomans pushing into the Caucasus' of Central Asia and firming their grip on Egypt in Africa, Germans expanding colonial gains by creating a continuous German state across about all of South Africa, Japan taking control of European pacific holdings and trying to force China into basically a protectorate, Australia/Canada/New Zealand/South Africa all developing national identities and using the war as justification for true independence, dozens of Middle Eastern tribes tearing the Ottoman Empire apart for independence, Slavs fighting for independence and unification from the Austro-Hungarians and the Russians trying to enforce such, etc.
This type of global participation was unprecedented and you will never find a war like it: Belgium, Romania, the United States, Australia, India, South Africa, the Ottomans, Mideastern Tribes vying for independence, Hejaz, Japan, Cuba, Costa Rico, Siam. 65,000,000 combatants would participate in the war and 37,000,000 people would die. It was not a European war between European powers for European goals it was a global war between global powers for global goals with significant global fighting between non-negligible sovereign global peoples -- the African, Middle Eastern, and Asian theaters alone justify this point imo without even touching America or Europe!
I also wrote about this topic in this thread here where I go into more depth about the African Theater and why it was like no other theater in Africa before it along with quashing some misconceptions. I'll quote the particular parts I want though:
The point is is that this was a war which changed everything and affected everyone like never before. South Africans, Indians, Australians, Chinese, Japanese, Germans, Arabs, Kurds, Armenians, Egyptians, Moroccans, Portugese, French, Indo-Chinese, Brazilians -- they were all directly affected by this war and by the fighting of it as quasi-independent actors. They all sent thousands and at times millions away to go fight.
It wasn't just "some European war" it was a European war that bled into North Africa and the Middle East in terms of heavy fighting. It was "some European war" that prompted United States and Japanese intervention. It was "some European war" which brought millions of Indians and Australians and Canadians and South Africans to willingly go fight and by 1918 they were not fighting as Brits they were fighting as Indians, Australians, South Africans, and Canadians -- something totally unique from, say, colonial forces clashing in the Napoleonic Wars. Japan and China's relationship would mature throughout this conflict and can be directly linked to the Sino-Japanese Wars of the future as Japan tried to posture upon China. Pacific Islanders, as said below, along with French and British colonials throughout Asia, India, and Africa all alike would find their national identities and their justification for separation through this war. The entire modern Middle East would be born from this war throughout the partitioning and rebellion in the Ottoman Empire. The United States would leave its isolationist bubble as the #1 industrial power and become part of the worlds congregation of "Great Powers".
That's really what separates it from every other global conflict before it (though the 7 Years' War and Napoleonic Wars are the only ones which can really be shoehorned into that category) -- it was not the Brits fighting in Southwest Africa they were Boers, Rhodesians, and Zulu's. It was Indians going to fight for Britain, not Brits. You see where I'm going with this? Nonetheless even if we go beyond this providing material support alone constitutes direct involvement and impact. That's really the point. Only a select few people in the world were totally escaped from the realities of this war whether it was direct fighting or economical unlike in these previous conflicts which were, essentially, European wars fought for European goals between European powers.
Where I got all these silly ideas from:
Peter Wilson, The Thirty Years War: Europe's Tragedy
John Lynn, The Wars of Louis XIV, 1667-1714
Christopher Clark, Iron Kingdom: The Rise and Downfall of Prussia, 1600-1947
David Chandler, The Campaigns of Napoleon
Hew Strachan, The First World War: Volume I: To Arms (specifically his chapters about 'the Dark Continent', the African campaigns)
According to the Oxford English Dictionary the term "world war" only entered English just a few years before the First World War (most likely from the German term Weltkrieg). It was defined as a war involving important or major nations.
So basically the First World War/World War One was the first war after the definition entered English to meet the definition.