Plantations owners are unable to export cotton during the civil war because blockage of the ports in south and encroach the areas of cotton growing areas.
Step-by-step explanation:
During the time of civil war, the crop cotton was one of the most valuable crop but there came a time when the exports of this crop had to be stopped and it had a huge impact on the foreign trade of the United States of America.
The reason for this was that the ports in the south got blocked in the war and the areas where the cotton was grown also got intruded by the opposition which could not let the cultivators grow the crop and affecting the cultivation.