In 1900 Europe was mainly divided into empires, kingdoms, principalities, duchies and a few nations that had claimed independence from the empires as their influence over them had waned over the years.
There were three major powers that dominated central, eastern, and south eastern Europe:
Ottoman Empire (Turkey) controlled parts of the Balkans.
Austria-Hungary (Hapsburg Empire) dominated central Europe
Russia ruled eastern Europe including Poland, Estonia, Latvia and Lithuania.
Turkey had once been a great empire, the Ottoman Empire, that controlled much of the Middle East and a significant part of South Eastern Europe, an area called the Balkans that included Greece, Serbia, Bulgaria and Romania.
Some of the Balkan states had gained their independence during the 19th Century. Ottoman power over the other Balkan states had weakened even more by the start of the 20th Century.
Ottoman influence over the Middle east was diminishing and, despite still controlling a vast expanse of territories, Turkey had become referred to as 'The Sick Man of Europe'
As Ottoman power weakened in the Balkans both Russia and Austria-Hungary tried to take advantage of it to extend their influence in the area.
The Austrian Empire was ruled by the Hapsburgs, a family with strong links to the other royal families of Europe including those of Prussia, Russia, Great Britain and Spain.
In 1867 the Hungarians had forced Austria to accept them as equal partners in the Hapsburg Empire and they had obtained some degree of self-rule.
Nationalism was becoming a very strong influence and many other nationalities were seeking independence from Austria-Hungary, especially in the Balkans.
The Russian empire was truly enormous. It stretched from Europe all the way to the Far East and the Pacific Ocean.
The empire was composed of various different nationalities and religions. Many of them were Muslim who had the Sultan of Turkey as their religious leader. Russia had to tread very carefully in any dealings with Turkey, as the Sultan had the right to call on the Muslim people to fight a holy war or Jihad. Russia never conscripted Muslim people because they were afraid of arming them.
During the 19th century Britain and France had both sided with Turkey in south eastern Europe and the Crimea to stop the Russians taking over the Balkans.
It promoted distrust between the various empires and small nations.
Competition between Austria and Russia caused tension in the Balkans.
It fostered 'Nationalism' - smaller countries developed a national identity and wanted to break free from the ruling empires and govern themselves.