The answer you're looking for is D. The individual states.
Well, as far as I remember. I'm sorry if I am incorrect.
The balkans The declining powers and collapse of the Ottoman, otherwise the sick man of Europe, empire made the soviet to focus their interests to the Balkans. this was especially after the japanese invasion and acquisition of Manchuria. This renewed interests in the Balkan states sparked the conflict that brought about the wars.
-Growth of ethnic nationalism throughout Europe and Middle East
The idea of the need of a "pure race" or of races of usurpers in the countries were getting common.
-Colonial groups looking for independence from imperialistic powers
This alone was more than reason for many to attack others from their own country. The problem is that the line is always blurry when it comes to decide the targets of the attack and who are actually the supporters of the enemy that deserve to be attacked. In the end, many just decided that just being against the cause was enough to add someone to the casualties.
-Spreading of communism and socialist ideas throughout the world
This enough generated many problems with the war between classes and the very troubling ideas of non existence of private properties and many other things that led straight up to physical conflicts, abuse of power and so on.
An arms race is when one country increases its army because others did.
An arms race is a competition between two or more states to have the best armed forces. It is done by means of competitive acquisition of military material, military spending or the number of people who serve in the army.
There is always a competitive nature to this buildup, hence the name race.
Some examples of an arms race are :
- The naval arms race between Germany and Britain from 1897 to 1914. It involved the costly building competition of Dreadnought - ships.
- The Cold War nuclear race between the United States and the Soviet Union. It led to large spending on nuclear missiles and the stockpiling of vast nuclear arsenals.
Hope This Helps! Have A Nice Day!!