For years, the Sahara was an obstacle for Europeans while Africans used the desert as a highway. Which conclusion is supported by this statement

The conclusion that is supported by the statement is : Desertification reduced the amount of arable land available to Africans and Europeans

Since the land couldn't be used to grow Crops, the ancient European does not see African Land as a region that is worth to conquer. Even until today, the modern African only used Sahara as an highway