What was the geographical obstacle of the Silk Road's trade with Africa?

The geography of the Silk Roads then is a complex interaction between the physical and climate zones of mountain, steppe or grasslands, and river valleys and oases which often are bounded by uninhabitable desert. Thus populations could be dispersed (in the grasslands) or concentrated in the oases and river valley

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whose power in the senate is equal to the power of the speaker of the house?

the tallest building in the western hemisphere and the sixth tallest building in the world