NOTE: large sections of this text are adapted from http://www.ehistory.com. See it for more details.
What Was It?
The War of the Roses was a civil war in England that lasted from 1455-1487. These thirty years of warfare were even more destructive to England than the Hundred Years War had been in the previous century. (Most of the fighting in the Hundred Years War took place in France, which meant most of the military damage affected the French peasantry rather than the English. In the War of the Roses, most of the fighting occurred in England, and thus the loss of life and property was much greater for English citizens.) It was a struggle to claim the throne between the families descended from Edward III and the families descended from Henry IV. The last Angevin ruler, King Richard II died without an heir. He had been overthrown and murdered by Henry IV (Henry Bolingbroke, who was of the House of Lancaster through his father John of Gaunt). Henry IV's descendants and their supporters were the Lancastrian faction. The other branch, descended from Edward IV, were associated with families in the North of England, particularly the House of York and Richard of York. They are called the Yorkist faction.
What's All This Stuff About Flowers?
The exact image of warring flowers was a late invention, and the general idea of each rose being a factional symbol originates in Shakespeare’s day. In Renaissance literature, writers linked the House of York with a white rose and the House of Lancaster with a red rose. For instance, in Henry VI, Part One, Act II, scene iv, lines 25-135, Shakespeare depicts the minor lords as choosing their factions symbolically by plucking either white or red roses from a garden. The play dates back to 1592 or so. For instance, in lines 124-128, we read the following:
Warwick: And here I prophesy: this brawl today,
Grown to this faction in the Temple garden,
Shall send, between the Red Rose and the White,
A thousand