Russia was the least industrialised empire, but potentially the strongest because of its size and large population. They joined this “Entente Cordiale” (Friendly Agreement) as they wanted influence over their fellow Slavs in the Balkans. Austria-Hungary, which was made up of many different nationalities, had difficulty in keeping the empire united. A particular problem was the independence of the Slav country of Serbia from the Ottoman Empire in 1878. They feared that this would be an example to other Slavs in Austria-Hungary to seek their independence. So naturally, Russia supported Serbia and other Slav countries against Austria-Hungary.
Germany, which was created in 1871 from separate German states after its defeat of France, and capture of the provinces of Alsace and Lorraine. France wanted revenge for the loss of Alsace and Lorraine to Germany. It had a large colonial empire and so was also suspicious of German colonial ambitions.
Britain at that point was one of the most industrialised and wealthiest nations in the world with the largest colonial empire. Britain needed a stronger navy than its rivals to protect this empire and protect itself. By 1900 Germany was challenging Great Britain as the main industrial power in Europe. They saw possession of overseas colonies a large status symbol, Germany’s ruler, Kaiser Wilhelm II also wanted Germany to have its own empire, its “place in the sun”. Germany resolved to gain as much territory as possible. They colonised territory in southern Africa (now Namibia) which no-one really wanted as it was useless desert but it did create anger in Britain as Germany's new territories were near South Africa with its huge diamond and gold reserves.
A second issue that caused much friction between Britain and Germany was Germany's desire to increase the size of their navy. As a result, a naval race took place. Both countries started spending vast sums of money to create battleships. All this did was make relations between the two countries even more turbulent.
The Great Powers of Europe were now divided into two opposing alliance systems. These alliances were defensive. However they were secret treaties so the rival powers did not know this and feared that they were aggressive treaties aimed against them.
All that was needed to spark of a potential disaster was one incident, and that incident occurred in Sarajevo in July 1914 with the assassination of Franz Ferdinand, the heir of the Austrian Empire. Although there was no hard evidence that Princip was acting under orders from the Serbian government, Austria blamed Serbia. Frantic diplomatic effort gave Austria a guarantee of German backing. With this support Austria now felt secure enough to deal with the Serbian problem once and for all. It gave Serbia a ten-point ultimatum that would effectively have made Serbia part of the Austrian Empire. The Serbs could not possibly accept it. When the Serbs asked for time to consider, Austria refused and declared war on 28th July, 1914. The slide to all-out war had begun.