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A particularly frequent, annoying and nonsensical alternate history cliché.
In a word: No, they don't have to. While similar conflicts are certainly not impossible or implausible, WWI and especially WWII were trigerred for very specific reasons with both deep and short-term historical roots. The very existence of WWII is dependent on the outcome of WWI and the period following it (in our history, the inter-war period).
Though many military advances similar to the ones in OTL WWI are made in the Portuguese Civil War of the 1910s, the war itself isn't as diplomatically and geopolitically far-reaching as WWI, due to its confined scope. Thus, the world doesn't really experience an all-out global war until the early 1930s, when the simply named Great War errupts.
Ed's depiction of a 1930s Great War was praised by many members of the board for its believability - it wasn't a carbon copy of WWI and/or WWII tactics and technology, but reflected the somewhat alternate level of military knowledge and technology that existed at that point in the timeline (it was more comparable to the level we had in the OTL late 1920s). Even the start of the Great War is rather original, as it erupts via a combined attack by the Empire of Japan on Taiwan.