Britain’s role in WWI was the result of a series of events beginning in the 19th century, the period of European imperialism. Major European powers, including Britain and France, competed for territory outside of Europe.
The scramble for Africa, in particular, involved the partitioning of African territory across European powers, granting Egypt to Britain, Morocco to France, and parts of east and southwest Africa to Germany. This competition fueled rivalries between major European powers, particularly between Britain and Germany as Germany’s naval power expanded as well as between Britain and Russia as Russia expanded into China. These tensions erupted with the assassination of Archduke Franz Ferdinand by a Serbian nationalist. Following the assassination came a domino effect that involved allied countries entering the war to protect promises they made to each other prior to the assassination.
Prior to WWI, Britain was concerned with Belgian neutrality and maintaining peace. Tensions between Britain and Russia existed, but eventually the Entente Cordiale and Anglo-Russian Entente were signed in an effort to maintain peace and unite against the enemy forces of Germany and Austria-Hungary. Britain entered the war in order to protect Belgian neutrality and out of loyalty to France, intending to protect both itself and smaller nationalities from German aggression. France, Britain’s ally, also fought to protect itself from German aggression, and felt enthusiasm and confidence in its decision to go to war because of support from the British, who have proven their loyalty to France. Germany, enemy of Britain, resisted all accusations, and responded with nationalism and reasons for why they had no choice in the matter, saying that their geographical location forced them to wage war.
Ultimately, however, Germany is responsible for the start of WWI. Little effort was made from its leaders to prevent war; those leaders repeatedly encouraged war and wrongly blamed Russia in the process.