What was the significance of Britain declaring war on Germany in 1914

It was the start of World War 1.

Explanation:

Great Britain declaring war on Germany was a result of German refusal to remove troops from neutral Belgium.

On August 4th 1914, Great Britain declared war on Germany ... In fear of being surrounded by the might of Russia and France, Germany had put into being the Schlieffen Plan in response to the events that had occurred in Sarajevo in June 1914. By doing this, the German military hierarchy had doomed Belgium to an invasion