Final answer:
President Lincoln was impressed with General Ulysses S. Grant following his strategic victory at the Siege of Vicksburg, which contributed to his promotion as General-in-Chief of the Union armies.
Step-by-step explanation:
President Abraham Lincoln was impressed with General Ulysses S. Grant’s success at Vicksburg. The siege of Vicksburg was a significant turning point during the Civil War, resulting in the Union's control over the Mississippi River and splitting the Confederacy in two. Grant's strategic encampment and trench warfare, along with his troops' efforts in digging and tunneling, led to the Confederate surrender mainly due to starvation from the blockade, rather than from direct battle losses. This victory not only secured Grant's reputation but also demonstrated his capacity for tenacious and effective leadership, capturing Lincoln's attention and leading to Grant's eventual promotion as General-in-Chief of the Union armies.