I'm not 100% sure but it could be: Voluntary Exchange takes place between buyers and sellers:
(btw I copied and pasted from the question so I didn't take any content :D)
Fort Sumter was the location of the first battle of the Civil War. Several southern states had already seceded from the Union, marking the beginning of political conflict, but Fort Sumter was where the military conflict/the Civil War technically began.
Through agriculture using the Euphrates river
The answer is Poland, Romania and Bulgaria were all Eastern block countries.
