The crusades have been called history's most successful failure because:
these wars bring about the fall of rome.
the crusaders could not reclaim jerusalem, but they did protect constantinople.
although the crusaders captured the holy land, they were unable to create democratic reform.
the crusaders failed to hold jerusalem, but the conflict sparked political, social, and economic growth in western europe.

C. Although the Crusaders captured the Holy Land, they were unable to create democratic reform.

Explanation:

Crusaders were nothing but a name given to a series of religious conflicts that was sanctioned by the Latin Church in the medieval period. Amongst them the best known are the campaigns in the Eastern Mediterranean. The purpose of which was to recover the Holy Land from the Muslim rule. And this as one of the biggest reason why Crusaders are considered as a successful failure. They were successful because they brought in many desirable changes. But they are also considered as a failure as they failed to achieve their original goal.

a.   it resulted in widespread unemployment.

your answer would be a) no nation can be economically self-sufficient.

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