WWI and WWII are standouts in their category for their scale and geographical extent. They are considered global conflicts because, even though various parts of the world (much of Africa and Latin America (and western Europe?)) saw no direct involvement, they felt indirect economic and politics effects.
However, it leads me to wonder what were the most ‘global’ wars of earlier decades or centuries, in terms of global impact during the actual wartime (rather than in subsequent years).
I think you need to read up on Africa and W Europe in WW1.
On topic, the Seven Years War and the French Revolutionary and Napoleonic Wars saw fighting in large parts of the globe. War of Spanish succession saw fighting in S America and the future United States.
The various Rome v Persia conflicts saw most of the civilised world outside of China involved, though less direct fighting out side of their border regions.
The Battle of Qarqar in 853 BC involved pretty much the entire ancient worlds nations less China.
You can make a similar argument about the Nine Years War (1688-1697). Or even the Thirty Years War (1618-1648). Those wars also saw battles fought in Europe, India, Africa, and the Americas. Basically once European countries became global imperial powers, any war fought between them would be a global war.
But these were all wars in which European powers were fighting each other albeit often doing so in non-European theaters. The first war in which a non-European power fought as a significant power along with various European powers was the Napoleonic Wars (assuming you accept the war between Great Britain and the United States as part of that war).
I don’t think it wins the “most” award by any criterion, but the American Revolution was more international than expected. French and German (primarily Hessian) involvement was known, as well as some individuals like Kociuszko. But it also led to wars between Britain and the Dutch Republic, as well as Britain vs. the Kingdom of Mysore (India).
The wars of Genghis Khan and his successors were not really global in that the New World was not involved at all and there was no naval component, but they did reach well into China, involved an African power (the Mamluks) and stretched into Europe.
I vote Napoleonic also. Especially if you count the War of 1812 as part of the conflict since it has just as much relation to the rest of the conflict as a lot of other wars that are considered as one such as the 30 years war.
However I would say Western Asia was heavily involved in WWI. The Ottoman Empire was on the side of the Central Powers, leading to Gallipoli.
And then there were the campaigns between the Ottomans and the Germans on the one hand, and on the other hand the British, French and Russians, assisted by local forces, in various locations in Ottoman territory.
The net result was the dismemberment of the Ottoman Empire, followed by British and French League of Nations “mandates” in Palestine, Syria, Lebanon, etc.
The new borders were straight-lines drawn by the Imperial powers (sorry; League of Nations benevolent mandatories) which [del]ignored local intérêts and ethnic divisions[/del] took grand geo-political factors into account.
The Balfour Declaration was another major outcome, setting the course for the foundation of Israel.
All in all, the effect of WWI on West Asia was immense, and we are still seeing the effects today.
The Nine Years’ War and the Thirty Years’ War were indeed largely just European powers fighting each other, sometimes outside of Europe. But the Seven Years’ War had significant involvement from non-European powers. Most notably, a large number of Native American groups in North America (Abenaki, Ottawa, Wyandot, and several others) fought during the war; there’s a reason it’s known as the French and Indian War in the United States. The Mughal Empire (which was admittedly in decline at that point) was a significant player in the Indian theater as well.
The Guerra de la Independencia of Spain from the French became several Guerras de la Independencia: Mexico, Colombia (later split into several), Centroamérica (intended to copy the US, instead each of its “component states” rapidly became its own nation-state, except for Guanacaste which joined Costa Rica), etc. It’s a war which created new sides as it raged on.
Much more importantly, West Asia was the site of fighting throughout the First World War. In Sinai and Gaza. The Levant. The Dardanelles. Mesopotamia. All places saw actions by the British, White Dominion and Indian forces against the Turks. So “no involvement”, except for the massive multiple, multi year campaigns.