The Inca empire compreended a large part of west South America during the 14th and the 15th century, until it was conquered by spain. The "capital" of the empire was the city of Cusco, in Peru.
In the 15th century, there was the Inca Civil War between two brothers for the throne of the empire, and diseases such as influenza and typhus had spread across South America. With this, the power of the empire weakened and it was conquered by Spain in 1572.
I think the correct answer from the choices listed above is the first option. The two events which weakened the Inca empire prior to the spanish conquest are civil war and diseases. Hope this answers the question. Have a nice day.
