Describe the motivation behind Britain and France's ultimate declaration of war on Germany?

The motivation is that Britian and France got angry when they found out that Germany invaded Belgium which was the first ever battle and start of the First World War (Battle of Liege). Germany invaded Belgium because they wanted to invade France inspired by The Schlieffen Plan which means they charge at France at lightning speed while Russia gets ready for war since they're so big and clumpy and then also charge Russia at lightning speed. But that plan failed since Belgium was strong enough to hold to Germans back. Austria - Hungary got angry at Serbia since they might have assasinated Ferdinand so they declare war on each other. Germany attacks the other countries fearing they might get involved too since France, Russia, and Britian are allies with Serbia.

Explanation:

2018 means 2018 ce or common era

there have been other eras too including bce, which included way more years.