Why did the arms race help to cause World War 1?

The Arms Race was a race to build the biggest army, navy and air force in preparation for looming conflict. All countries except Britain and Germany tried to build colossal armies. Britain and Germany instead tried to build up their respective navies, as Germany wanted their navy to beat the size of Britain's.

In Germany they had the biggest army, and it was the best trained and most powerful out of all armies involved in World War One. However Britain, being completely surrounded by water, had large powerful navy helped to keep the empire safe. Also, it wasn't until after WW1 that Air Force really played its part, as planes were still rather early in development and could not fly from country to country and accurately bomb a target.

THAT DOESNT ANSWER THE QUESTION

All the countries began a "contest" for who was the best by doing all that stuff. They all really wanted to "show off" their weapons etc. So because of that everyone(countries) are thinking that the other is going to attack them and it kept going on and on. Because of that the countries started making alliances with other countries. When the Archduke of Austria-Hungary was killed and Austria-Hungary declared war on Serbia. Then because of the alliances almost all of Europe was in the war.

hope that makes stuff clearer :)