Why was George McClellan so important during the civil war. What did he do. Short paragraph please!

George McClellan was a U.S. Army engineer, railroad president and politician who served as a major general during the Civil War.

abraham lincoln  (february 12, 1809  – april 15, 1865) was an american statesman, politician, and lawyer who served as the 16th  president of the united states  from 1861 until  his assassination  in april 1865. lincoln led the nation through the  american civil war, its bloodiest war and its greatest moral, constitutional, and political crisis.[2][3]  he preserved the  union,  abolished slavery, strengthened the  federal government, and modernized  the u.s. economy.

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