Question

what nation came to rival Britain's economic output right before World War 1

Answer 1

maybe Germany I'm not sure if this is right or not

Answer 2

Germany came to rival Britain's economic output before World War I.

The Germany after its unification became a strong country under Otto Van Bismark in late 19th century. It began to expand its imperial power by colonizing other nations and thus came into the clashes with the economic interests of Britain. So there began a naval race between the two nations which strained their relations and hampered the process of peace just before WWI.