How as Abraham Lincoln as a leader during the Civil War? How did his presidential decisions influence the outcome of the war? What struggles did he face as a leader?

As a leader, in general, most historians give Abraham Lincoln high marks for his leadership style and decision making. Although susceptible to bouts of depression—profoundly affected by the war—Lincoln always made an effort to present a positive and upbeat outward attitude which no doubt belied the enormous pressure he felt to maintain the Union. From all accounts, Lincoln's management style was to gather all the facts, to then query experts (even those who disagreed with him), and to finally form a logical conclusion from which to base his actions. Once committed, President Lincoln never wavered from his decisions or the accountability for his actions. He never blamed anyone for his failures and had an enormous sense of humility.
Three examples demonstrate how Lincoln's resolve resulted in Union victory and the United States remaining united. The first defining decision was appointing Ulysses S. Grant to general and placing him in charge of Union troops. Grant replaced a long succession of disappointing, indecisive, and somewhat inept Union military leaders, who had earned their rank from being part of elite families but whose military abilities were not up to the challenge.
Almost immediately, Grant was able to organize and mobilize troops to begin to strategically defeat Confederate forces. Although Grant was renowned for his military prowess, his empathetic approach to negotiating the terms of surrender with General Lee may well have been his greatest triumph. Ably managing the terms and not taking an adversarial position with Lee, Grant allowed Lee's Confederate troops to return to their previous lives without fear of prosecution. Grant even allowed them to keep their horses and weapons and guaranteed them safe passage as they returned to civilian life. This may well have been the most critical key in bringing the Union back to one piece. It was Lincoln who was willing to change generals amid battle, and his apt choice for the position demonstrates his leadership.
The second example was Lincoln's Emancipation Proclamation. The debate around the abolition of slavery was fierce in his own cabinet, with several key advisers in opposition to the proposal. Many felt the Proclamation would prolong the war by further provoking the South and by fundamentally enacting presidential powers that were not clearly articulated in the United States Constitution. Lincoln listened patiently and waited to secure the needed support for his announcement.
Though he did not have full support for the Proclamation, with many of the dissenters asking the president to amend the document to be less controversial, Lincoln issued the Proclamation without a change on January 1, 1863. The Emancipation Proclamation clearly articulated Lincoln's stand on slavery and established a precedent for future presidents to claim war powers under the Executive Branch.
While there are several other examples of Lincoln's leadership, the Gettysburg Address may be the best example. Lincoln's unexpectedly short speech, which was barely five minutes long (the person speaking before Lincoln spoke for more than two hours), was able to begin the healing process of reunification and restated the fundamental values that created the United States. Initially panned by the crowds at Gettysburg, once it was published in newspapers across the country, the Gettysburg Address had a profound and lasting effect on everyone who read it. The speech was both a tribute to the men who had lost their lives in battle and a call for peace and reconciliation. Again, Lincoln demonstrated his leadership of promoting unity above self-interest and the country above politics.
In many instances, Lincoln demonstrated a unique blend of folksy wisdom, high idealism, and an ability to make everyone feel as if they had a personal relationship with the sixteenth President of the United States. These qualities are in demand and are exceedingly rare among politicians in our modern time.
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https://teachingamericanhistory.org/library/document/lincoln-as-a-leader-of-men/