Below is an excerpt from a letter written to General McClellan, commander of the Union Army. Why did Lincoln have McClellan replaced as commander of the Union Army?

My dear Sir:
You remember my speaking to you of what I called your over-cautiousness. Are you not over-cautious when you assume that you cannot do what the enemy is constantly doing? Should you not claim to be at least his equal in prowess, and act upon the claim?...
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• The men's morale was at an all time low, and McClellan was known for rushing in to battle
• McClellan was too hard on the men, and he lost several thousands in battle
• General Burnside was a close, personal friend to Abraham Lincoln, and he had more battle experience than McClellan
• Abraham Lincoln was disappointed that McClellan did not follow through and was too cautious

Abraham Lincoln had McClellan replaced as commander of the Union Army because he was disappointed that McClellan did not follow through and was too cautious.