Graham Bartram, The Story of Scotland's Flags, XIXth International Congress of Vexillology Proceedings, 2001 (full text here).
Robert E. Bonner, Colors & Blood, 2002.
Devereaux D. Cannon, The Flags of the Confederacy, 1994.
W.G. Perrin, British Flags, 1922. (Available here; four relevant pages here.)
Geo. Henry Preble, Origin and history of the American flag, vol. II, ed. 1917. (Full text of the section on confederate flags here.)
The United States of America (USA) were born in 1776, when 13 rebellious colonies seceded from the British crown. By 1860, the USA consisted of over thirty states. Late that year, South Carolina seceded from the Union, and first seven, then four more "slave states" formed the Confederate States of America (CSA). Two more states, Kentucky and Missouri, were divided on the matter but the Confederacy admitted them nonetheless, making the "rebellious states" equal in number to the former "rebellious colonies": thirteen. Virginia, Georgia, North Carolina and South Carolina were rebel states as they had been rebel colonies. Two slave states, Maryland and Delaware, did not secede. Four years and countless casualties later, the southerners had been brutally forced back into their unhappy marriage with the Yankees.
While it lasted (1861-1865), the Confederacy had its own government, president, capital, currency and flag. Its first national flag, the "stars and bars", proved a tragic mistake. From a distance, it looked so much like the enemy's "stars and stripes", that soldiers and commanders got confused on the battle field. As a result, confederate general Pierre Beauregard decided to create a separate "battle flag" for military use. He chose a design which William Foster Miles had submitted to be the national flag, but which had been rejected, in spite of Miles chairing the selection commitee. Today, Beauregard's battle flag is best known in the following form:
Historical examples may be square instead of oblong, have a crimson instead of red background, less than 13 stars, stars six-pointed or gold, no white fillet separating blue and red, coloured borders added. Here and in other confederate flags, stars reflected the number of states seceded or admitted to the confederacy (3, 7, 11, 12, 13) or the total number of slaveholding states (15). In a number of successive posts, we will try to reconstruct how this design came into being.
Let's also say a few words on secession proper.
When the Southern States seceded from the United States of America in 1860 and 1861, they believed that they were acting in a perfectly legal and acceptable manner. The Constitution of 1787 had been drafted by delegates from the States and had been voluntarily ratified by the people of the several States. No State had been forced into the union, and any State whose people did not wish to join the union could go its own way. Logically, it followed therefore that any State could also voluntarily leave the union when its people believed that the union was no longer serving its purpose or establishing justice and/or insuring domestic tranquility. (Cannon, p.1-2.)After the war, confederate rear admiral Raphael Semmes put it thus:
I have never warred against the institutions of my country. I have always cherished an affection for the principles of the old Constitution and the old flag; and it was only when the old flag ceased to represent those principles, that I consented to war against it. One of the first acts performed by the Provisional Congress that met at Montgomery was to adopt the old Constitution as the Constitution of the Confederate States. (...) As, then, our war was one for the old Constitution, it follows, logically, that we were arrayed against the old flag, because it had ceased to represent that constitution. (Preble, II, p. 509.)