What was a factor in African trade across Sahara

Camels were a huge factor in trade across Africa! They usually traveled in groups to trade called caravans.

The West Africans exchanged their local products like gold, ivory, salt and cloth, for North African goods such as horses, books, swords and chain mail. This trade (called the trans-Saharan trade because it crossed the Sahara desert) also included slaves. Slaves would be taken to southern Spain as household servants.

Explanation:

the doctrine of nullification recommended that states living inside the union have the one-sided, inalienable ideal to void any law made by the national government that could be esteemed illegal.

the united states was shaped based on a general agreement among its individual states. hence, it is inferred that under the hypothesis of invalidation, since the states are the establishment of the union, they have the ability to referee and disprove unlawful laws.

to act quickly in times of danger to the united states

because you have to act quickly if you want to live/survive.