Many people with only minimal interest in late medieval British history have gained a new appreciation for the War of the Roses because George R. R. Martin has said that it inspired him. His "Song of Ice and Fire" series of books has been made into a popular TV series as "Game of Thrones." The real War of the Roses was between two branches of the royal family, called the Yorks and the Lancasters, whose names inspired Martin's Starks and Lannisters. If you look at Martin's map of Westeros, you will see that it is the same shape as Great Britain (though flipped), with The Wall up around where Hadrian's Wall stretched across Britain during the late Roman Empire.
The name, "War of the Roses," sounds like something sweet. It was not. It was an extremely nasty civil war, fought with gunpowder, cannons, and conscripted foot soldiers. At its most basic, it was a war between two related families, both of whom thought that the English crown should be theirs. It started in 1455, only two years after the English had finished losing the Hundred Years' War with France, and lasted, with on-and-off fighting, for the next thirty years. Let's just say that if you liked warfare, fifteenth-century England was the place to be.
We tend to think of the crown as descending in a tidy way from father to oldest son, but royal inheritance never was tidy in England. The difficulties that led to the War of the Roses started innocuously enough with King Edward III (1327-1377) and his four sons, Edward, Lionel, John "of Gaunt," and Edmund. So far, so good, heirs and back-up heirs.
Edward, called "the Black Prince" (he was proud of his special black armor), was a great war leader during the Hundred Years War but did not live long enough to succeed his long-lived father. No problem--he had a son who succeeded as Richard II.
But Richard II died childless. So the crown went to his first cousin, John of Gaunt's son Henry IV. This is the line that became known as the Lancasters, whose emblem was the red rose. But wait! you say. How about Lionel and his heirs? Well, that's exactly what Lionel's descendants wanted to know. But Lionel had not had sons, only daughters, which is why his line was skipped over.
The Lancasters hung onto the throne for the next two generations, but Lionel's descendants remained grumpy. Then, Lionel's great-granddaughter married the duke of York, a descendant of Edmund, who you will remember was King Edward III's youngest son, and whose emblem was the white rose. The war was on.
Initially the Yorks won, but then they turned on each other. Richard III (a York) became king in 1483 after the mysterious death in the Tower of London of his young nephews, his royal older brother's sons, who one would have thought were heirs to the throne. Ever since then, Richard III has had a bad reputation, although there has been a concerted effort to rehabilitate him. Richard's bones were recently found in England under a parking lot.
The above is a simplified version of a very messy and complicated series of conflicts. The point is that relatives can hate each other much more bitterly than they hate non-relatives. The war did clear out an awful lot of England's aristocracy, especially branches of the royal family. The eventual winner was neither a York nor a Lancaster, but Henry Tudor, who was Welsh, and who became Henry VII after he defeated Richard III in 1485.
On the one hand, this shows that winning battles is more important than being the "rightful heir," especially as no one had been able to agree for thirty years who was the "rightful heir." But Henry VII did have connections to both Yorks and Lancasters, a detail he made sure everyone recognized. His mother was a descendant of a younger son of John of Gaunt, and hence could be called a Lancaster, and his wife was a sister of the York "princes in the Tower." At this point, everyone was so exhausted that no one tried to raise any more issues.