In 1917, Germany, determined to win its war of attrition against the Allies, announced the resumption of unrestricted warfare in war-zone waters. Three days later, the United States broke diplomatic relations with Germany, and just hours after that the American liner Housatonic was sunk by a German U-boat.
Reliable because it's not always sunny
The reason that led to the rise of the domestic slave trade was the regional specialization in labor production. The South had a much higher demand of slaves for the labor-intensive cotton plantations. This demand for labor pushed up the prices of the slaves, intensifying the trade.
