To accurately identify which statement reflects a major effect of the causes shown in a diagram, I would need to see the specific causes mentioned in the diagram you are referring to. However, I can provide some insights on each of the options you've listed:
a. Conquest of Central America - This could lead to the establishment of new territories and influence over local cultures.
b. Unification of the empire - This typically indicates a strengthening of political control and cultural cohesion among diverse groups.
c. Rise of first Andean cultures - Suggests a cultural and societal development that could lead to advancements in agriculture, technology, and trade in the region.
d. Devastating civil wars - This generally results in weakened states, loss of life, and fragmentation of societies.
If the diagram highlights events that led to negative outcomes, d. devastating civil wars could be a likely major effect. If it indicates the expansion of influence or territory, then options like a. conquest of Central America or b. unification of the empire might be more appropriate.
For a more precise answer, please provide additional context or information about the specific causes shown in the diagram.