The intended meaning is:

The Somalians greeted a law with defiance which is similar to some other defiance. This other defiance occurred in USA in the 19th century.

There has to be two occurrences of "defiance" in the sentence - one for the Somalian incident and the other for the USA incident (to which the Somalian incident is compared.)

In option D, the pronoun "that" creates the second copy of defiance - the defiance that occurred in USA.

However in option A "defiance" occurs only once. One instance of defiance cannot refer to both the Somalian incident and the USA incident. Hence option D is better than option A.

The following example will clarify further why option A is wrong:

I made a similar drawing that depicted the true condition of the nature. Here the drawing I made shows the true condition of nature. To what my drawing is similar is not known.... (similar to option A above)

I made a drawing which is similar to a drawing that showed the true condition of nature. Here the other drawing showed the true condition of nature- I made a drawing similar to that other drawing. (similar to option D above)

Thanks sayantanc2k

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In A a single use of ‘defiance’ is meant to refer to two separate instances of defiance. Same error in E.
In B ‘which’ is used incorrectly.
In C ‘what’ is used incorrectly.

So D is the right answer.