Wars of the Roses
During the Hundred Years' War, the kings of England got into a big fight about who should be king, which caused a long civil war in England. One side was the Lancaster side, which took a red rose as its symbol.In 1399 AD, at the beginning of the civil war, Richard II was king of England - that was the Lancaster side.
The other side was the York side, which took a white rose as its symbol. Richard's cousin Henry - another of King Edward III's grandsons - killed Richard and made himself King Henry IV. That was the York side. When Henry IV died, his son succeeded him as Henry V, who fought in France in the Hundred Years' War but got killed.
Henry V's son Henry VI succeeded him in turn, but he suffered from mental illness and couldn't rule very well. He ended up losing the Hundred Years' War and all of England's land in France, so he seemed like a loser and people thought they might do better with a different king.
Richard, Duke of York thought he would be a good choice - and, like Henry V, Richard was also Edward III's great-grandson. Richard never succeeded in becoming king, but when Henry VI died Richard's son Edward IV did become king, and after Edward IV died his younger brother ruled as Richard III. Richard III fought with his army even though he was born with scoliosis that twisted his back. It looked like the House of York had won the Wars of the Roses.
But the Lancastrian cause was taken up by someone almost totally unrelated to any earlier king, from a new family: Henry VII, whose grandfather had been married to Henry V's widow. Henry got major military support against Richard from Anne, who was ruling France. In 1485, Henry VII killed Richard III at the Battle of Bosworth Field and became king.
Henry VII was a very strong king, and he weakened the power of the rich men so that he could stay in power. He made Parliament stronger, but not the aristocratic parliament. Henry VII worked mainly with the new lower-class part of Parliament, the House of Commons, rather than with the House of Lords. (It's traditional for strong kings to get their power from ordinary people against the rich people - compare the tyrants of ancient Athens, or Augustus in ancient Rome.)