After a series of failures, Germany decided to maintain a defensive approach towards the Central powers by the end of 1914.
Germany started to concentrate in developing their military rail roads to bring the raw materials for making weapons as the British already blocked the ammunition supply via sea route.
Germany created a trench barrier in France border to prevent Allies invasion. France was very keen on breaking this trench barrier and regain their lost territories to Germany.
British was in a research to invent a machine that would be capable of crossing those trench barriers. It leads to the invention of military tanks.
The combined Allied forces finalized a decision to attack Germany from different routes like Balkan peninsula or via Germany's Baltic coast rather than using tanks in French border.
Allied forces launched continuous premature failure attacks and failure experiments on Germany. Germany played defensive in most of the attacks. However at the end Allied paid 242,000 men against the defender's loss of 141,000 men.
A part of German army made offensive attack to relieve Russian pressure on the Austro-Hungarians to their south on the Eastern front.
Famously called as the Gorlice attack, launched in May 1915, it achieved success beyond all expectation by total collapse of Russian army and their retreat far into Russia.
Central Power's victory was because of superior artillery firepower from Germany.
Dardanelles Campaign(A menace from Turkey):
While Allied forces were attacking Germany in the west, Russians were threatened by Turks in the eastern front.
Early in January 1915, Turkey became a threat to Russia in the Caucasus(mountain region lying between Black sea and Caspian sea) region.
Russia appealed to British for some naval help. Britain naval forces invaded to capture Turkey's Gallipoli peninsula(western shore of the Dardanelles strait). By late April 1915, Britain took the troops from Egypt, Australia, and New Zealand to land on Turkish shores.
British halted for a while on the shores to gather as many troops as possible. Turks took this as an advantage and gave a successful attack with the help of land forces from local navies.
Dardanelles campaign thus came to an end and in January 1916 with Allied forces staging a full retreat from the shoes of the peninsula with 250,000 causalities.
In 1914 the center of gravity of World War I had been towards the Allied forces. In 1915 it got shifted towards Central forces. Let's wait to see what 1916 had got for us!
Also read : Why Turks performed mass killing of Armenians?