World War I or the First World War (28 July 1914 – 11 November 1918), often abbreviated as WWI, was one of the deadliest global conflicts in history. The first decade of the 20th century saw increasing diplomatic tension between the European great powers. This reached breaking point on 28 June 1914, when a Bosnian Serb named Gavrilo Princip assassinated Archduke Franz Ferdinand, heir to the Austro-Hungarian throne. Austria-Hungary held Serbia responsible, and declared war on 28 July. Russia came to Serbia's defense, and by 4 August, defensive alliances had drawn in Germany, France, and Britain. German strategy in 1914 was to first defeat France, then attack Russia. However, this failed, and by the end of 1914, the Western Front consisted of a continuous line of trenches stretching from the English Channel to Switzerland. The Eastern Front was more fluid, but neither side could gain a decisive advantage, despite a series of costly offensives. Attempts by both sides to bypass the stalemate caused fighting to expand into the Middle East, the Alps, the Balkans, and overseas colonies, bringing Bulgaria, Romania, Greece, and others into the war.
Based on the provided paragraph give a bullet list of the names of the countries (regions) which took part in WWI and their reasons?
The countries and regions that took part in World War I (WWI) and their reasons are as follows:

- Austria-Hungary: because their heir to the Austro-Hungarian throne, Archduke Franz Ferdinand, was assassinated by a Bosnian Serb named Gavrilo Princip.
 
- Serbia: because Austria-Hungary declared war against them.

- Russia: because they wanted to defend Serbia.

- Germany, France, and Britain: because they were allies with the countries already engaging in the war.

- Middle East, the Alps, the Balkans, and overseas colonies, bringing Bulgaria, Romania, Greece, and others: because the Eastern Front of the war was more fluid, but neither side could gain a decisive advantage. Both sides had attempts to overcome the stalemate leading to the war expanding into these regions and countries.