D is your answer. it gives a more specific answer than the other choices, plus it is true. Slavery has been around since Jesus time, so that's way longer than the 1500s
a policy of returning land to a country that it belonged to in the past: They are concerned about the possible irredentism of the minority in their midst. His program was full of irredentism and ultra-nationalism.
It can be both A and D however A is the more accurate because the question specifies international conflict