Before the Spanish conquest, the Incan Empire faced a series of challenges that weakened it significantly. Among the options provided, D, diseases and war is the most accurate.
Prior to the arrival of the Spanish, the Incan Empire experienced internal conflicts, as well as the devastating effects of European diseases, such as smallpox, which significantly reduced the population and weakened the empire's social structure. The combination of these factors created an environment of instability that the Spanish conquistadors exploited during their invasion. While drought and famine (option C) also affected the empire, the immediate impact of diseases and warfare on the Inca's ability to resist conquest was more critical at that moment.
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