Question

on august 4, 1914, great britain declared war on germany. why?
great britain had an alliance with serbia. it needed to protect serbia after germany declared war.
germany declared war on great britain first. great britain declared war back.
great britain wanted to protect france from a german invasion.
germany invaded belgium. belgium had an alliance with great britain.

Explanation:

Great Britain declared war on Germany on August 4, 1914, primarily because Germany invaded Belgium. Britain had a treaty (the Treaty of London 1839) guaranteeing Belgium's neutrality, which obligated Britain to respond to the invasion.

Answer:

Germany invaded Belgium. Belgium had an alliance with Great Britain.