Answer:
Were the necessary outcomes of the political vacuum created by the toppling of the monarchy.
Explanation:
There is a subject-verb problem in the original sentence, there is a plural noun and then there is a "was" that is incorrect.
Options A, B, and D repeat both the same subject-verb problem. While option C corrects this trouble. It presents a new one by giving responsibility to the monarchy about the vacuum. The correct sentence is option E that refers that the vacuum was created because of the fact that the monarchy was toppled.
I hope this answer helps you.