I found this pretty cool site that has a flash map of WWI. It shows the how the war started and proceeded.
The Alliance system during the WWI brought together Germany, Austria-Hungry, and Italy as The Triple Alliance. Against The Triple Alliance were The Triple Entente; England, Belgium, France, Russia, and Serbia. During the war Belgium, Serbia, Austria-Hungry, and Italy played minor roles in the war. So towards the end the war narrowed down to Germany fighting against England, France, and Russia.