Pretty difficult, you'll need some major luck for the Russian Republic, Lenin at least needs to butt out, I dunno, Russians gain access to German battleplans, a major offensive aimed at the Austro-Hungarians smashes the southern front and buys a few extra weeks/months for the Russian heartland.
The German Kaiser Offensive needs to work even better, Paris is seized but the only way Britain 'loses' is having the BEF totally destroyed during a failed Dunkirk operation, so a French fall, Britain humiliated leading to far more American led war effort from then on