Final answer:
During the early years of the Civil War, President Lincoln had to replace his generals due to their inability to defeat the Confederates and their personal disagreements with the president.
Step-by-step explanation:
During the early years of the Civil War, President Lincoln was forced to keep replacing his generals for several reasons. One major reason was the Union army's inability to defeat the Confederate forces under General Robert E. Lee. This lack of success made it clear that some of the generals were not capable of winning the war. Furthermore, Lincoln had personal disagreements with some of the generals, such as General George B. McClellan, who not only lacked aggressiveness in battle but also criticized the president's decisions. As a result, Lincoln had to seek replacements who could deliver decisive victories for the Union.