Why the counterfactual stops in the 1920s

The scenario cannot be extended confidently beyond the Washington treaty era. A fragmented Germany, a surviving Russian Empire, altered Polish borders, different alliances, and continuing naval construction would interact in ways that rapidly multiply uncertainty. Britain would also lose unified Germany as a central European buffer against France and Russia, while Italy is poorly placed to replace it. An independent Poland might absorb territory from German successor states and emerge as a regional power, adding another branch to the scenario. Projecting those effects into later decades would require complex diplomatic and economic models whose outputs would still rest on numerous guesses. Keeping the Gallipoli divergence small allows historical reference points through the early 1920s, but moving much farther becomes fiction rather than constrained historical analysis.