On Jan. 18th, 1486. Henry VII, the newly proclaimed King of England married Elizabeth of York. Henry VII had made sure to wed his new bride after he was proclaimed and crowned King. Why did he do this? Well, perhaps it is because his new bride had a far better claim to the throne than he did. He, actually, was not the best candidate for King. His claim to the throne came from his mother's line. Margaret Beaufort was descended from John of Gaunt, third son of Edward III. Margaret was born to one of the children John and his mistress, Katheryn Swynford, had before their marriage. Though the children were later legitimized, they were barred from the succession. Thus, Henry really had little claim to the crown. His wife, on the other hand, was the only surviving child of King Edward IV. She was the heir to throne after the mysterious disappearance of her brothers, Edward V and Richard, Duke of York (also known as the Princes in the Tower).
Despite all this, Henry was crowned King because he won it, defeating Richard III in battle. Thus, he was "King by Conquest." Marrying Elizabeth of York after he was victorious ensured that he ruled in his own right, not by marriage.