Wars of the Roses
The thirty-year civil war between two branches of the English royal family that destroyed the old nobility and put the Tudors on the throne.

Between 1455 and 1487 two branches of the English royal family, the House of Lancaster and the House of York, fought a series of short and brutal campaigns for the crown. They killed one king in battle, deposed three more, and wiped out much of the old nobility. That last part is what mattered most. England came out of the wars with a monarchy so strong that no great lord could challenge it again.
Nobody at the time called it the Wars of the Roses. The name caught on in the nineteenth century, helped along by Walter Scott, and only the Yorkists used a white rose with any regularity.
Why the crown was up for grabs
Henry VI became king at nine months old. He grew into a devout and politically hopeless adult, lost every French possession his father had won, and in 1453 suffered a mental collapse that left him unresponsive for more than a year. Richard, Duke of York, who had a strong claim of his own and a long grievance about being kept out of power, took over as protector. Queen Margaret of Anjou fought him to protect her infant son's inheritance.
England was also full of armed men with nothing to do. Great lords kept private companies of paid soldiers, and thousands of veterans had just come home from the lost war in France. The first fighting, at St Albans in May 1455, was less a battle than an ambush in a market town that killed the king's leading advisers.
Twenty years of reversals
The war ran hot in short bursts and went quiet for years at a time. At Towton, fought in a snowstorm in March 1461, the Yorkists destroyed the Lancastrian army in what was probably the bloodiest day of fighting ever on English soil. A newsletter written a week later claimed 28,000 dead. The true figure was almost certainly lower and still enormous for a country of about three million people. Edward IV took the throne.
Then Edward lost his most powerful ally. The Earl of Warwick, remembered as the Kingmaker, changed sides in 1470 and briefly put Henry VI back on the throne. Edward returned, won at Barnet and Tewkesbury in 1471, and Henry VI died in the Tower that May, almost certainly murdered.
When Edward died in 1483 his brother took the crown as Richard III, and Edward's two young sons vanished inside the Tower. That disappearance broke the Yorkist side apart. Henry Tudor, an exile with a weak Lancastrian claim through his mother, landed in Wales in 1485 and won at Bosworth Field when the Stanley family, watching from the flank, finally committed against the king. Richard III was killed in the fighting, the last English monarch to die in battle. Henry VII married Elizabeth of York, combined the two emblems into the Tudor rose, and crushed the final Yorkist rising at Stoke Field in 1487.
What Henry VII built
Henry won the peace with paperwork rather than battles. He confiscated his enemies' lands through acts of attainder, tied the surviving families to him with financial bonds that could ruin them if they stepped out of line, and enforced the laws against keeping private armies. A nobility that had spent thirty years killing its own members was in no condition to argue.
The result was a crown that could do things earlier kings could not. When Henry VIII broke with the pope in the 1530s, seized the monasteries, and rewrote English religion, no baronial coalition formed to stop him. The Tudors also spent a century reminding everyone how bad the wars had been, and the most successful piece of that campaign is still on stage: Shakespeare's history plays end with Richard III as a monster and Henry Tudor as the man who saved the country.