In a military history class, I was introduced to the concept that the US Civil war was considered "A war by amateurs" by many foreign observers due to the martial ineptitude and technological backwardness of both the Confederacy and the Union.
Are there any strong historical or contemporary accounts that support this claim?
Logistically, probably not too hot for either side but definitely worse in the south.
Martial ineptitude on the side of the Union for a long, long time during the war. Their general was an engineer with little practical experience in warfare and it showed. It took Lincoln a long time - longer than it should have - to find competent warfighters. The south was very adept at battle since the outset of the war and continued to adapt traditional tactics to changing technology up until the end.
Technological backwardness - no, the opposite. Both the north and the south employed state of the art equipment and experimental weapons with regularity. It was so cutting edge, and tactics were changing so quickly to adapt that nearly every country in Europe sent many observers to sit on the sidelines of the battles being as they were being fought to take notes and analyze what happened.
"martial ineptitude and technological backwardness" may be a stretch, but the simple fact was that the largest force the US Army had fought with prior to the Civil War was In the Mexican American War and those forces were less than 12,000 men. At the first battle of Bull Run each (roughly 90 days after firing on Ft Sumnter) SIDE had over 25,000. Nobody had any experience in moving or supplying (much less fighting) with such large forces.