Answer:
Correct answer is a. nationalism.
Step-by-step explanation:
Correct answer is A as it is a way how they wanted to create a national state, that will be free from influence of other empires that were surrounding them.
B is not correct as communism was an idea that spread across Russia during WW1.
C and D are not correct as imperialism and militarism were policies that were led by greatest European forces such as Germany.