What was a Trial by Ordeal and why were they used in medieval society?

The Union blockade, known as Winfield Scott´s Anaconda plan, was slowly strangling the Southern economy.

Explanation:

The blockade, proclaimed by Abraham Lincoln, required the monitoring of 3,500 miles of Atlantic and Gulf coastline. It was a powerful weapon and was very successful in the sense that thousands of ordinary freighters stopped calling at southern ports. The Southern cotton exports were choked off (hard currency for the Confederation) and on the military side it was Lee´s Southern army that nearly always was short of supplies.