The correct answer to this open question is the following.
I think irredentism is more valid than imperialism because irredentism is the valid claim of people or nations to a lost territory conquered in the past by imperialistic ideas.
Imperialism is the idea powerful nations have to conquer and expand territories. Once these territories were conquered, the land is split according to political and economic interests. That is when irredentism, comes into place. People have the legit demand to claim their lands back because they originally belonged to them.
