Final answer:
Ulysses S. Grant wrote to his wife with optimism about the waning will of the Confederates to fight. He played a critical role in bringing about the Confederate surrender at Appomattox Courthouse by recognizing their low morale and resources.
Step-by-step explanation:
The person who wrote to his wife expressing optimism and a sense that the Confederates lacked the will to fight was none other than Ulysses S. Grant. During the final phase of the Civil War, General Grant displayed a keen understanding of the deteriorating morale and capacity of the Confederate forces. In a dispatch, he commented on the Southern soldiers' desire for peace, and evidence suggests that he sensed victory was near as Confederate deserters reported the weariness of the men. Grant's strategic persistence and military campaigns contributed significantly to the Union's ultimate triumph. As the Union's military leader, he pushed the Confederacy to its limits, with his army repeatedly engaging Lee's troops in Virginia until the dire situation compelled the Confederate surrender at Appomattox Courthouse. Following the surrender, Robert E. Lee remarked on the overwhelming numbers and resources of the Union that led to the Confederacy's defeat.