Why did Great Britain declare war on Germany in World War 1?

Great Britain declared war on Germany on August 4, 1914, primarily due to Germany's invasion of Belgium. Britain had a longstanding commitment to defend Belgian neutrality, established by the Treaty of London in 1839. Additionally, the broader context of alliances and rising tensions in Europe contributed to Britain's decision, as it sought to maintain its influence and counter German expansionism. Thus, the violation of Belgian sovereignty prompted Britain to act decisively against Germany.