Which of the following led to increased tension in 1915?

It was due to 3 main topics:

• Economic rivalry - At the end of the 19th century Britain had the largest economy in the world and dominated world trade. However, by 1914 German industry was producing more iron and steel than Britain and was leading the way in new industries such as chemicals and cars. By 1913 Britain had lost ground to both the US and Germany.

• Imperial rivalry - France and Britain already had large empires but newer united countries of Italy and Germany were keen to build theirs. The result was that in the years before 1914 there was increasing competition between the great powers, more especially for parts of Africa. The Kaiser was determined to get Germany 'a place in the sun', in order to strengthen Germany's position as a world power.
• Military rivalry - In the years 1900- 14 the arms race developed between the main European powers to build up the size of their armed forces and armaments. As each country increased the size of its army and the number of weapons it held, it became more confident of success in a future was and more willing to test out its armed forces.