The Germans planned to invade France by going through Belgium because they could then form a “hammerhead” by going through Belgium and then invading Paris assuming that the rest of France would give up once the Germans invaded their capital at all their borders which were not defeated. They also expected Belgium to sit back and allow Germany to just go straight through their country.
It was crucial that Germany took over France in three weeks or less as they planned because if it took longer than those three weeks, Russia would be prepared for fighting against Germany in war and Germany’s army and then there would be none of Germany’s army over on the western front while their eastern front was being attacked by the Russians.
Germany had to capture the channel ports because if they didn’t, the British army would go over to France and help them by possibly providing them with supplies or even fighting for them because Britain had a much smaller yet much stronger army than anyone else so if they helped France by fighting off Germany, Germany wouldn’t have much of a chance of defeating France in time to get back to the eastern front to fight Russia.
Germany thought that it would take Russia six weeks to prepare for war so Germany allowed themselves to spend three weeks to defeat France so they could then have time to travel to the eastern front to defeat Russia before they were fully prepared for war, therefore giving them the advantage so they could invade Russia a lot easier and quicker.
Germany didn’t think their plan through very well because they thought that although Britain signed a treaty with Belgium in 1839, they could still go straight through Belgium without any trouble from the British to get to France because it was a long time in the past that they signed the treaty and Germany didn’t believe the British would go to war over a “scrap of paper”. But the British still signed it and so they had to protect Belgium from the Germans. Also Belgium had huge forts and walls on their border to prevent other countries like Germany invading them, but it was lucky for Germany that they had a secret weapon; the biggest cannon in the world, “Big Bertha”. For all Germany knew, Belgium could fight back and not allow Germany to go straight through their country to get to France. Another potential for Germany was that Russia could mobilise a lot quicker than the Germans expected. A man named General Joffre inspired the French armies to resist the German advance, and he rushed reserve troops to the front from Paris, using any form of transport available. He ordered that “a unit which can no longer advance must at all costs retain the ground it has gained and rather than retire, be killed on the spot”, therefore, that inspired the French armies to fight until the end and until they all die, if they do this, the Germans might get afraid and give up.