Can somebody help me with this ?

C. It discouraged the British from supporting the Confederacy

Explanation:

The British abolished slavery years before the US, so it would look very wrong for the UK to support the confederacy, who were the ones who preserved slavery.  This also wouldn't set well with the public which would erupt some protests across the nation, and the US also could've invaded Canada and that also would've been bad for the British because wars were expensive.

explanation: j

porter is writing economic history because he is focusing on the cost of developing vaccines.