The Germans planned to defeat the French through the use of the Schlieffen plan. The Schlieffen plan consisting of an attack on Russia, with France on Russia's side, Germany had to defeat France in the time it would take Russia to mobilize which General
Then we looked at allies. At the start of the war Germany, Austria-Hungary, and Italy were allied. But Italy said, “I don’t have to be part of this since you weren’t attacked,” and they changed sides.
In contrast to the historian Fritz Fischer who saw German war aims - in particular the infamous September Programme of 1914 with its far-reaching economic and territorial demands - at the core of the German government's decision to go to war, most historians nowadays dismiss this interpretation as being far too narrow. They tend to place German war aims, or incidentally all other belligerent nations' war aims, in the context of military events and political developments during the war.
The German government issued demands to France that it remain neutral as they had to decide which deployment plan to implement, it being difficult if not impossible to change the deployment whilst it was underway. The modified German Schlieffen Plan , Aufmarsch II West , would deploy 80% of the army in the west, and Aufmarsch I Ost and Aufmarsch II Ost would deploy 60% in the west and 40% in the east as this was the maximum that the East Prussian railway infrastructure could carry. The French did not respond, but sent a mixed message by ordering their troops to withdraw 10 km (6 mi) from the border to avoid any incidents, and at the same time ordered the mobilisation of her reserves. Germany responded by mobilising its own reserves and implementing Aufmarsch II West . On 1 August Wilhelm ordered General Moltke to "march the whole of the … army to the East" after he had been wrongly informed that the British would remain neutral as long as France was not attacked. The General convinced the Kaiser that improvising the redeployment of a million men was unthinkable and that making it possible for the French to attack the Germans "in the rear" might prove disastrous. Yet Wilhelm insisted that the German army should not march into Luxembourg until he received a telegram sent by his cousin George V, who made it clear that there had been a misunderstanding. Eventually the Kaiser told Molkte, "Now you can do what you want."   Germany attacked Luxembourg on 2 August, and on 3 August declared war on France. On 4 August, after Belgium refused to permit German troops to cross its borders into France, Germany declared war on Belgium as well.    Britain declared war on Germany at 19:00 UTC on 4 August 1914 (effective from 11 pm), following an "unsatisfactory reply" to the British ultimatum that Belgium must be kept neutral . 
Grey: What will America do if the Germans sink an ocean liner with American passengers on board?