In WWI, under the Schlieffen plan, Germany chose to initially take a defensive position with Russia and attempt to push into France first. This push, of course, brought them through Belgium, brought the British into the war, and ultimately resulted in stalemated trench warfare that would last for years. Meanwhile, on the eastern front, fighting proved to be more open and dynamic, with the Russians eventually collapsing on their own internal strife.
What would happen if Germany, instead, reversed this plan? What would happen if they simply held their own border with France and instead worked with the Austro-Hungarians to launch an offensive against the Russians first? Would they be able to keep Britain out of the war? Would they be able to prevent the Italians from siding with the Entente? Would France attempt their own offensive into Germany?