which factor most directly resulted in great britain entering world war i
History of the United Kingdom during the First World War The ostensible reason given was that Britain was required to safeguard Belgium's neutrality under the 1839 Treaty of London. The German invasion of Belgium was, therefore, the casus belli and, importantly, legitimized and galvanized popular support for the war.
World War I The war drew in all the world's economic great powers,[9] assembled in two opposing alliances: the Allies (based on the Triple Entente of the Russian Empire, the French Third Republic, and the United Kingdom of Great Britain and Ireland) versus the Central Powers of Germany and Austria-Hungary. Although Italy was a member of the Triple Alliance alongside Germany and Austria-Hungary, it did not join the Central Powers, as Austria-Hungary had taken the offensive against the terms of the alliance.[10] These alliances were reorganised and expanded as more nations entered the war: Italy, Japan and the United States joined the Allies, while the Ottoman Empire and Bulgaria joined the Central Powers.