With grey appear the countries that were on the side of the allies during World War 1 i.e. England, France, Russia, and with pink appear the countries that were on the side of Germany. Note that Italy was an ally of Germany till the very last moment, but she decided to remain neutral, and later joined the allies. With green the neutral countries.
The English were afraid that the Germans would reach the Persian Gulf through Austro-Hungary and the Ottoman Empire, and would get access to the oil of the Persian Gulf, and that they would threaten their most important colony i.e. India.
The Russians were afraid that the Germans and the Ottomans would threaten their oil at Baku, and they also wanted to destroy the Turks at the Strait of Bosphorus, in order to obtain access to the Mediterranean Sea.
The French wanted revenge from the Germans, for their defeat at the war of 1870-1871, and also wanted to take back the territories they lost at this war i.e. Alsace and Lorraine etc. Moreover, the British had promised to give the French some of the territories of the Ottoman Empire in case of victory.