Why did Great Britain declare war on Germany in 1914?

Answer: The declaration was a result of German refusal to remove troops from neutral Belgium. In 1839 the United Kingdom, France, and Prussia (the predecessor of the German Empire) had signed the Treaty of London which guaranteed Belgium sovereignty.

Explanation:

The declaration was a result of German refusal to remove troops from neutral Belgium. In 1839 the United Kingdom, France, and Prussia (the predecessor of the German Empire) had signed the Treaty of London which guaranteed Belgium sovereignty.

Great Britain entered war I on 4 August 1914 when the king declared war after the expiration of an ultimatum to Germany. The official explanation focused on protecting Belgian neutrality; the most reason, however, was to stop a French defeat that will have left Germany up to the mark of Western Europe.

(hope this answers your question) : D