Below is small snippet of text from the multiverse, from a 1950 US World History high school textbook, to be exact. Although it describes a war in the 20th century, the PoD or PoDs reach into the 19th century. What happened?
The Origins of the Great World War of 1922-1931
The World War is unusual in modern history in that the principal warring states were divided into at least four mutually hostile coalitions, which shifted on a regional basis and as the war progressed. These alliances were based solely on expedience and had no relationship to any ideological or political systems the warring powers may have shared. The war was not sparked by any single event or series of related events, but instead coalesced into a single worldwide conflagration from a number of initially unrelated regional rivalries, some of which had broken out into open hostilities as early as 1914. The ending date of the war is also somewhat arbitrary, as several civil wars and local conflicts not terminated by the Rome Peace Treaty of 1932 have continued to the present day (1950).
Although by 1922, virtually every major and minor nation was involved in hostilities, it can be reasonably argued that the prewar policies of three principal countries: France, Russia, and the United States, were most responsible for expanding a series of unrelated regional conflicts into a global war. France was actively expanding its empire in directions guaranteed to result in conflict with Great Britain and the United States. Russian expansion in the Balkans, Turkey, and central Asia was a threat to British, French, and Austro-Hungarian interests, and the increasing militarization of Alaska extended this threat to Great Britain in North America as well. The United States, while not overtly expanding in ways threatening the other major powers, had made it very clear since the 1870's that its policy was to regain its lost western territories by whatever means possible. This made American entrance into the war virtually inevitable once Britain and France became preoccupied with each other in other parts of the world.
In most respects, the most heavy responsibility lay with the French Empire, in that the policies of Napoleon III and his successors virtually guaranteed a war with Great Britain, and that a war between the only two powers with extensive worldwide colonial holdings would become a “world” war by default. Also, by aggressively seeking to bring most of western Europe under direct French control in a way which clearly impacted the security of the British home islands, France ensured that any war with the British Empire would not only be limited to far-flung and relatively unimportant colonial outposts, but would be waged within the European heartland as well. Finally, by fostering Mexican aggression in North and Central America, France had virtually assured war with the US and CSA, even had the US not been seeking to regain territories lost in the North American War.
Basic “alliance”structures by region. In all cases, none of these alliances were formalized :
Western Europe, including Mediterranean. Great Britain and a few minor European allies (Portugal, Sweden, Norway) vs. French Empire, Austro-Hungary and satellites. Noncombatant in this theater: USA, CSA, Russia, Mexico, Turkey
Eastern Europe/Balkans. Russia and Balkan satellites vs. Turkey, Austro-Hungary, and France. Great Britain was hostile to both sides, but essentially noncombatant in this theater, as was the USA and CSA
North America. USA and CSA vs France and Mexico. USA vs the British Empire. CSA noncombatant against England France and Great Britain hostile to each other but essentially noncombatant in this theater as their respective empires do not share common borders. Russia, Turkey, and Austro-Hungary noncombatant.
Central and South America. USA vs France and Mexico (both sides with client local states). France vs British Empire. Britain essentially noncombatant against USA in this theater except to defend existing colonies and interests. Russia, Turkey and Ausro-Hungary completely concombatant.
Asia/Africa. Essentially a free-for-all, with no permanent alliances among any states. Main hostilities: Great Britain and Turkey vs Russia in Asia and France vs Great Britain in Africa. Other powers essentially noncombatant except to defend existing colonial holdings and protectorates.
In addition to conflict among major nation-states and empires, events of the Great World War fostered a series of irregular rebellions and civil wars, including most notably the Slave Rebellions of the CSA, the Chinese Nationalist Revolution, The Boer Rebellion in South Africa, the War of Imperial Restoration in the Japanese Archipelago, and the Ghost Dance Wars of western North America. Some of these conflicts were initially instigated and abetted by one or another of the major warring nations, but all took on a life of their own following te 1932 Rome Peace Treaty. Some are still raging in the present day (1950)