WWI: Britain

Britain was engaged in the greatest war of modern times, one in which it military deaths were more than twice those it would suffer in World War Two. World War One may not have initiated democratic change, but it set its timing. Britain was the key country in the Great War. Germany was without doubt the most powerful continental power. Germany industry combined with the professionalism of the Germany Army meant that it could defeat either France and Russia and even the two countries combined. But defeating an alliance including Britain proved to be too much for Germany.
Had Germany prevailed in their initial offensive and defeated France, the War would have probably ended quickly. A protracted war of attrition, however, swung the advantage to the Allies because the powerful Royal Navy gave the Allies access to the resources of the Empire as well as neutrals like America. And it enabled the Allies the ability to blockade Germany, cutting it off from raw materials and food. The key conflict in World War I was the conflict between France and Germany which had historic roots but in modern terms began with Franco-Prussian War and the unification of Germany. Britain at times had sided with the German states when France was the dominant European power.
Many historians believe that the British alliance with France was a foregone conclusion given the rise of Germany and the threat of German domination of the continent. . British policy at the turn of the 20th century, however, seems curiously crafted to oppose German hegemony. Certain the British were firmly committed to maintaining naval superiority which was demonstrated by the construction of HMS Dreadnought and the even more powerful battleships that followed. When G invaded Belgium and France, the BEF  was such a small force that the Germans almost reached Paris and won the War.