Answer:
D. A division or separation of something into portions.
Step-by-step explanation:
Based on the given sentence, the main idea of the sentence is that the 'partition" of the Middle East after WWI is in most ways responsible for the emergence and frequency of the many conflicts. This means that the structuring of the land helps/ contributes to most of the turmoil in the nation.
Now, the word "partition" means something or anything that is separated or put into portions, smaller sections, or the changing of its structure and boundaries. It is the division of anything into many pieces.
Thus, the correct answer is option D.