The initial sides of the First World War took shape on August 4th, 1914, when Germany invaded Belgium. Belgium’s neutrality had been guaranteed by the United Kingdom in 1839, and so when Germany refused to leave the country, Britain declared war.
The pre-war British Army was numerically inferior to those of the great Powers of the continent. It had not instituted the practice of conscription, and so relied entirely on volunteers. As such, it took several months to raise and train the necessary forces to send an expeditionary force to France. However, when that force did arrive, the BEF played a critical role in stopping the German offensive into France. Further, the Royal Navy immediately set about implementing a blockade on Germany, preventing food from reaching the country. Britain also cut the diplomatic cables between Germany and the US, ensuring that all war news that reached America would be from a British point of view. However, Britain, like France, would be unable to break the stalemate in the west and would suffer horrendous casualties at the Somme and other battles for little ground gained. Her soldiers would also fight, along with men from the colonies, in Africa and the Middle East against German colonial forces and the Ottoman Empire. Here, Britain would see much more success, advancing into Jerusalem by the start of 1918 and occupying most of Germany’s African holdings. Germany, for its part, would attempt to break the naval blockade at the battle of Jutland. Although Britain did suffer heavier losses, Britain retained naval supremacy and continued to cut Germany off from world trade. The British naval blockade would prove to be decisive in the end, as the German Army, still on Belgian and French soil, would be forced to surrender by food shortages and unrest at home.
Although the German invasion of Belgium did provide the immediate pretext for war, Britain would likely have found another way to involve itself even if Germany had withdrawn from the country. The reason for this is quite simple; Germany’s industrial capacity had already far exceeded that of Britain and its land forces eclipsed the British Army in number and was equaled or surpassed in doctrine and training. Britain had to stop Germany’s rise, lest it challenge Britain’s supremacy on the world stage and supplant it as the dominant power. As always happens when the dominant nation is threatened, Great Britain did everything in its power to defeat its challenger and maintain its global hegemony.