When Henry, Duke of Lancaster, usurped the throne of his cousin Richard II in 1399, to become King Henry IV, he also usurped the rights of Richard's presumptive heri, the Earl of March. A strong king might hold a rival in check; Henry IV was not such a king, and Richard, Duke of York, who had inherited March's claim to the throne, raised an army to challenge him.
The Wars of the Roses, named from the symbols of the Houses of York and Lancaster, lasted intermittently from 1455 to 1466. York emerged victorious and, after surviving a renewal of the war in 1470-71, the dynasty was apparently secure.
However, a second usurpation, by Richard III in 1483, opened the way for a new challenge. The senior line of Lancaster was extinct, but there was a junior line, descended from the third marriage of John of Gaunt. Though the children of that marriage were born out of wedlock, they had been legitimized by royal charter in 1397. Their representative was Henry Tudor, Earl of Richmond.
On August 22, 1485 Henry Tudor defeated Richard III in battle on Bosworth Field, and became king. He was a cautious man and by the marrying the heiress of the House of York he strengthened his descendants' title to the throne.
