What did germany do to cause britain to join World War 1?

Germany's aggressive actions in the early 20th century, particularly its invasion of Belgium in August 1914, prompted Britain to enter World War I. Britain had a longstanding commitment to protect Belgian neutrality, established by the Treaty of London in 1839. When Germany violated this neutrality as part of its war strategy, Britain declared war on Germany on August 4, 1914, in defense of Belgium and to uphold its commitments. Additionally, the broader context of rising tensions and alliances in Europe played a significant role in Britain's decision to join the conflict.