For the challenge above with minimal butterflies:
1913: Have Bulgaria avoid the Second Balkan War with a pod between the First and the Second Balkan Wars.
1914: After Archduke Franz Ferdinand's assassination and WW1 started, the Russians failed to get Admiral Essen to return to Kronstadt on time and Russia proceeded to sink the Swedish Navy, causing the Swedes to join WW1 against Russia. The Russians transferred troops in Finland and Petrograd to defend Finland, but the proximity of Finland to the Russian capital of Petrograd would divert Russian troops to Finland from the Caucasus and improve Ottoman performance for the Central Powers. Otherwise, WW1 in 1914 proceeded more or less as in otl.
1915: The Ottomans would perform better in the Caucasus and the transfer of Russian troops from the Caucasus to Finland would keep Italy neutral. Russia would recapture Finland for itself. The Ottomans, with a better performance for itself in the Caucasus, would be able to do better against Russia and at Gallipoli. Bulgaria would join the Central Powers as in otl and the Austro-Hungarian 5th Army not being needed in Italy and being used in Serbia would result in more of the Serbian Army being destroyed in Serbia in 1915.
1916: With the neutrality of Italy, the Austro-Hungarian Army would be able to defeat the Brusilov Offensive and avoid territorial losses (at least in the July-August phase of the offensive) to the extent of encouraging Romanian neutrality. The Russian troops staying near Romania would be transferred to continue the Brusilov Offensive, but the German, Austro-Hungarian and Ottoman troops used in Romania would be able to defend the Carpathians and stop the Brusilov Offensive. The Bulgarians, without the destroyed Serbian and neutralised Romanian Armies, would be able to use the Struma Offensive as an opportunity to neutralise Greece and the Entente by taking Kavala and Salonika, forcing the Entente troops, without Serbian and Greek soldiers and without Salonika as a resupply route, to intern themselves together with Venezelists in neutralised Greek territory. The Ottomans would take more territory from Russia despite Russia taking more territory from Finland and Sweden. Rest of WW1 as in otl.
1917: The Germans would go for unrestricted submarine warfare as in otl, but the Swedish and other Scandinavian minorities would make it a bit more difficult for the United States to send troops to France. The German resources used in Caporetto would be used in Verdun and divert the otl British and French troops in Italy to Verdun in a failed attempt to defend the city after the previous year's battle there. After the French loss of Verdun, the Italians and the Spanish joined the Central Powers and diverted American and French troops to the French-Italian border. Romania would be neutral for WW1. Rest of WW1 as in otl.
1918: with Russia, Serbia and Montenegro surrendered, Romania and Greece neutral and the Bulgarians and Austro-Hungarians strong and having nothing else to do, the Spring Offensive, aided by Italians, Spaniards, Bulgarians and Austro-Hungarians in diverting the Americans to Southern France, would succeed in knocking out France and defeating the Entente from WW1 through advances from southern France to Paris diverting French troops and causing a German victory at the Second Battle of the Marne. Central Powers victory.