Germany's invasion of Belgium on August 4, 1914, marked a significant turning point in the early stages of World War I. Germany had devised the Schlieffen Plan, which aimed for a quick victory by invading France through Belgium. However, this breach of Belgian neutrality, which had been guaranteed by the 1839 Treaty of London, provoked international outrage. Belgium, a small and neutral country, stood firm against the German advance, marking its military resolve by mobilizing its forces. The Belgian government formally declared war on Germany as a demonstration of its sovereignty and independence.

The United Kingdom, having pledged to protect Belgian neutrality, responded swiftly to the invasion. On the same day, the British government declared war on Germany, thus entering the broader conflict that would engulf much of Europe. This declaration was driven not only by legal obligations but also by a sense of moral duty to support a smaller nation against aggression. Prime Minister Herbert Asquith and Foreign Secretary Edward Grey played crucial roles in this response, rallying public opinion and parliamentary support for the war effort.

In contrast to the actions of Belgium and Britain, the United States declared its neutrality, reflecting a desire to avoid being drawn into the conflict and to focus on domestic issues. President Woodrow Wilson emphasized this neutral stance, promoting peace and diplomatic solutions despite the unfolding war in Europe. The complexity of allegiances and the intricate web of treaties that characterized the period laid the foundation for a conflict that would last for four years, resulting in unprecedented levels of destruction and loss of life across continents.