One cause of the outbreak of World War I was caused by

1:The outbreak of the Russian Revolution

2:Rising tensions among European powers

3:The killing of a Serbian National

4:The invasion by Germany of Belgium

I think it's 3

https://www.google.com/search?q=immediate+cause+of+WWO&oq=immediate+cause+of+WWO&aqs=chrome..69i57.4954j0j7&sourceid=chrome&ie=UTF-8

Let us know if you change your mind or not.

I changed my mind. I now realize it is 2.

Right.

The cause of the outbreak of World War I was a combination of several factors, but one of the main causes was rising tensions among European powers. To understand this, we need to look at the historical context leading up to the war.

One factor that contributed to these rising tensions was the assassination of Archduke Franz Ferdinand of Austria-Hungary, heir to the Austro-Hungarian Empire, by a Serbian nationalist in June 1914. This event, known as the killing of a Serbian National, sparked a diplomatic crisis between Austria-Hungary and Serbia.

Austria-Hungary issued an ultimatum to Serbia, which Serbia partially accepted. However, this did not satisfy Austria-Hungary, and they then declared war on Serbia. This led to a chain reaction of alliances and mobilizations among European powers, as countries began aligning themselves with either Austria-Hungary or Serbia.

Germany, a major power at the time, then declared war on Russia, which was an ally of Serbia. This was due to the outbreak of the Russian Revolution, which destabilized the Russian government and made them unable to support their ally. Germany also launched an invasion of Belgium as part of their military strategy, which violated Belgian neutrality and drew other countries into the conflict.

In conclusion, the outbreak of World War I was primarily caused by the rising tensions among European powers, with the killing of a Serbian National and the invasion of Belgium by Germany as significant events that contributed to the escalation of the conflict.