The core of the alliances in WW1 was France-Russia and Germany-Austria/Hungary, and that's largely inflexible post-1900, but we can flip one of the big boys: alienate Britain from Russia, hard. This is fairly easy to do:
Dogger Bank goes worst-case due to the Russians having better aim (or more likely, just getting lucky) and the trawler fleet is trashed - more deaths, more destruction, and especially more outrage. The Russians manage to grovel their way out of a war declaration, but relations with Britain are utterly ruined - enough so that it's an open secret the British are providing direct support to the Japanese in the Russo-Japanese War, not that the Russians can do anything other than stew.
The poisoned relations mean that the British look more favorably on anyone willing to oppose the Russians, which benefits the Triple Alliance, and Kaiser Willy is *just* competent enough to accept the gift horse, modifying the naval buildup to avoid antagonizing the British. When some damn fool thing in the Balkans triggers war between Austria-Hungary and Russia, Italy honors her alliance and the Germans, needing to keep the British happy, avoid Belgium.
Germany, Austria-Hungary, and Italy beat the stuffing out of France and Russia in a much shorter Great War, while the British make money hand over fist selling supplies and the Ottomans are able to conduct reforms, strengthening their state. The Russians are crippled (only outside help props up the Tsar, but nobody wants to unleash the chaos that his overthrow would trigger), and the French, despite wanting revenge over the harsh terms imposed, are unable to really get anything going.
The British Empire remains strong, the German Empire is preeminent in Europe without truly dominating the continent, the Ottomans are able to keep the Middle East under control and peaceful, and the Japanese claim French colonial possessions in Asia, a large enough prize to appease their desire for expansion. France is revanchist, but lacks the strength to do much, while the Russians are hemmed in by stronger powers (Germany to the west, Japan to the east, the Ottomans and British to the south) and forced to settle for internal improvements.
Eventual decolonization is less messy, as the British, Germans, and Japanese (the French possessions being split between all three) boast stronger, wealthier empires and are able to leave on their own terms. It's not nicer, but it's more peaceful.