Which term refers to a nation's tendency to expand its armed forces and acquire new and better weapons?

a. imperialism

b. militarism

c. progressivism

d. conservatism

The correct answer in this case would be militarism (b). The reason why this is the correct answer because a nation's tendency to expand its armed forces and acquire new and better weapons is also exactly that - militarism.

Other answers here wouldn't be correct because they have different meanings. The only thing that would come close is imperialism which has some similarities but is used in different contexts.