What northern tactic destroy morale in the south after the defeats at gettysburg and vicksburg

It was the speech Abraham Lincoln gave also known as the Gettysburg Address. It made the people realize that it was not just a collection of individual states; it was one unified nation.

Total Warfare: its best example was Sherman's March to the Sea, where his troops destroyed railroads, bridges, warehouses, crops, telegraph lines, all forms of infrastructure. It prevented sending reinforcements and supplies to Lee's troops, starving them out, and it served to weaken the morale of the serving troops, making them fear for the safety of their families back home.

d. migration of french settlers into english colonies