Do you mean the Confederate flag (the stars and bars) or the battle flag of the Army of Northern Virginia (St. Andrews Cross)?
Back again, sounds like some people need a little history lesson.
The south suceeded over economic freedom and, yes, that included the use of slaves. The south was producing most of the farm goods of this country especially cotton. The northern factory owners wanted to keep the price of cotton low so they could make a profit. The southerners wanted to sell their product to anyone who could buy it. The politician in Washington DC passed tariff after tariff making it more expensive for England, France, and other European countries to buy southern cotton. One faction of the new Republican party was very much anti-slavery. They were called radicals. Lincoln was their candidate among the other four contenders for the White House. States in the south promised to suceed if Lincoln was elected. With the vote split five ways Lincoln won with a plurality. Shortly thereafter South Caroline suceeded. Followed by six other states which is important when talking about the flag that represented the Confederacy. Things stayed quiet for awhile and the flag was raised over a new country. The Star and Bars had seven stripes of red and white and a field of blue in the left hand corner. That was the flag of the Confederacy.
South Carolina demanded that Lincoln remove troops from the soil of their country, Fort Sumter. Lincoln refused and South Carolina fired upon the fort until they struck their colors and retired.
Lincoln called for an army to be formed for a period of 90 days to put down the rebellion. Talk about being misinformed and underestimating your enemy! Many military commanders refused to march troops through another country (many felt their states were much like countries) such as Virginia to attack South Carolina. Men such as Stonewall Jackson and Robert E. Lee resigned their commissions than follow such an order. Frankly, Lincoln was left with the B team when it came to generals at that point. Virginia organized an army to protect itself and the Confederacy. This army was known as the Army of Northern Virginia. Many of them wore Federal blue uniforms and their flag (the stars and bars) looked very much like the Federal flag. They came up with their own flag which was St. Andrews Cross on a field of red with 13 stars in the cross. This was not the Confederate flag, this was the flag of the Army of Northern Virginia. A military flag that only represents the fighting men of that unit. Every Confederate state had it's own flag. Understand that the Confederacy did not invade the north until 1863 when Lee thought he could end the war by fiegning an attack of Pennsylvania (Gettysburg) and then wheeling around to capture Washington DC. The south did not want to overthrow the government in Washington. They wanted the north to stay our of their country.
As for slavery, it was still legal in many northern states until the end of the War between the States. The Emancipation Proclamation only ended in slavery in the states in rebellion.
Many historians have also come to the conclusion was on the way out in the south. It was becoming economically untenable. Free labor is more productive than slave labor.
So slavery would have ended in about 20 years and 1,000,000 people would still be alive. I wonder how the people felt in some small town when they heard the army was coming. They hid their women, their farm animals, and their treasure because the army was coming. Then the army approached, the army flying the Stars and Stripes! The army men arrested innocent people, hung some for information (a popular practice), and shot some out of hand. The treasure was found and stolen, the women violated in some cases, and the animals slaughtered for food. Talk bout hate, the hate came from the North.