Who started trench warfare?

Germany was fighting a two-front war with France and Britain in the west and Russia in the East. German forces dug in for the winter where they had halted. The British and French, meanwhile, lacked the resources to mount large scale offensives, so they dug in and prepared for offensives in 1915. Gradually a 400 mile line of static trench defenses existed forcing the development of trench warfare tactics.