How did the Sahara desert affect trade?

Rivers have trade corridors which are a passageway for trade ships with cargo. Deserts have a bad terrain so in order to trade across the desert you would have to have a vehicle that can withstand...

Desertification of many places of world especially semi arid regions of Europe

It doesn't. Rattlesnakes are only found in North America. The Sahara desert is in Africa.

Lack of civilization, lack of organised infrastructure (roads, electricity, schools, hospitals), temperature extremes, wind, lack of grazing for animals, lack of water for agriculture etc.

Yes.