Lee, Joseph Johnston, and "Stonewall" Jackson.
The country had been avoiding the disputes that would later become the causes of the civil war for decades. Once South Carolina voted to secede from the Union on December 20th,it set a fatal precedent, one that threatened to unravel the Union.
The aforementioned reasons sparked the occurrence of the Civil War. The southern states felt that Lincoln was against slavery and also against the South. Abraham Lincoln said they did not have the right to leave the United States and sent in troops to stop the South from leaving. The South argued that each state had rights to secede and leave the Union whenever they wanted — they claimed that states should decide whether they want to pass laws or not, as the states were themselves important individual regions.
The key issues were slavery, different political ideologies, right of the people, and economic reasons.