Henry's ascendancy cannot be credited to his bloodline. Though history enthusiasts argue to this day regarding the strength of his claim, Henry himself made little attempt to justify his grasp at power that way. He claimed his rich Welsh heritage through his grandfather, Owen Tudor. His mother, Margaret Beaufort, did have a bloodline that eventually reached back to Edward III through John of Gaunt's mistress, but this was hardly a fact that would place him near the throne.
Except that it did.
Henry may not have had much royal blood, but with noble cousins killing each other on battlefields for the last 30 years of the Wars of the Roses, few stronger options existed. Yes, there were other relations, but each remaining family line had some weakness in it before it reached back to a solid royal root. In the end, the fitness of his blood didn't matter, because Henry Tudor won the crown through conquest, just as his distant relative William of Normandy had.
Why was England in this state where distant royal bastard lines were considered for kingship? It all started with the many sons of Edward III.
Edward III's heir gave all signs of being a medieval knight quite capable of following in his father's footsteps. Probably for his dark armor, or possibly because of acts committed in France, this younger Edward became known as the Black Prince. Unfortunately, the he died shortly before his father, leaving a young Richard II on the throne surrounded by uncles and cousins who coveted power.
Richard II was forced to abdicate by his cousin, Henry Bolingbroke, who was the son of John of Gaunt - another of Edward III's sons. When he became king in 1399, Henry IV set the stage for the Wars of the Roses that would clear the way for the Tudor dynasty. Considered the Lancastrian branch of the Plantagenet royal family due to John of Gaunt's title as Duke of Lancaster, Henry's reign almost immediately came under fire from the Mortimer family, which had ties to Edward III's second son, George, and fourth son, Edmund. Henry proved capable of quelling those rebellions, and the country rallied behind his son when he became Henry V.
Henry V was considered everything that a medieval king should be. He pressed to reclaim lands in France that had previously been in English hands under Henry II, the original Plantagenet king. No one felt a need to point out that his father had been a usurper. Things might have gone on swimmingly had Henry V not died too young, leaving a 9 month old Henry VI as king.
Henry VI was raised and advised by his uncles, and never seemed capable of shaking his need for their instruction - or at least someone's instruction. His mother was Catherine of Valois, daughter of Charles VI of France who was quite insane when he died. Both Catherine and Henry would eventually demonstrate signs that they suffered the same malady.
The young widow Catherine made a scandalous second marriage to a servant of her household. His name was Owen Tudor. This connection gives Henry Tudor one link to the royal family, but not his strongest one. It did, however, give him his Tudor name that would go down in history.
Henry VI proved completely incapable of ruling, becoming victim to those who would manipulate and mislead him before falling into long trances of madness. Soon the Duke of York was pressing his claim as heir presumptive, and calling Henry unfit for duty. Were it not for the strength, or some would say stubbornness of Henry's queen Margaret of Anjou, that may have been an end of things. Richard of York may have been king as agreed by Henry when he made him his heir, disinheriting his own young son.
Margaret took the fight to the York supporters, and many noblemen answered her call in defense of their anointed king. Over the course of three decades, generations of earls and dukes, many of whom could trace their family tree back to reach Edward III, were left dead on fields of battle. By the time Henry Tudor defeated Richard III at Bosworth, there truly were few left who had a better blood claim, and none had struck down the last king in battle.
Before we reach that moment though, we must give attention to England's York kings. Richard Duke of York who had originally taken up the fight was killed in the battle of Wakefield in 1460. Instead of giving them victory, the Lancastrians now were faced with a vengeful Edward Earl of March, now Duke of York. The 17 year old heir of York was the epitome of a soldier, standing tall and golden above the men around him and looking every bit the Plantagenet king that Henry VI was not.
When he became king in 1461, he continued to battle the supporters of Henry VI for over a decade. The fighting did not come to an end until 1471, when the Lancastrian prince was killed in battle and Henry VI was disposed of in the Tower. With nobody to threaten him, Edward IV could have enjoyed a long and peaceful reign. Like his predecessor, Henry V, Edward made the mistake of dying too young and leaving the future vague and turbulent.
His heir was 12 year old Edward, who was immediately proclaimed Edward V with his uncle Richard of Gloucester as protector. Without debating whether Richard was the one who murdered Edward and his brother, we will simply say that it was Richard who was crowned while the young sons of Edward IV disappeared. Their fate as the Princes in the Tower is one of history's greatest mysteries, and was another key slipping into place opening the way for Henry Tudor.
Whether Richard III had done away with the boys or not, enough people questioned his innocence and his motivation in taking his nephew's crown. He faced rebellion from the Duke of Buckingham, who also had a fair share of royal blood, and the constant threat of the followers of Henry Tudor from exile. When Henry landed in Wales, Richard likely saw it as a chance to rid himself of an annoyance. Since Richard's wife and son had both recently died, he had nobody to follow him if he died in battle besides the sons of his sisters and young Edward of Warwick, son of Richard's brother George.
One of those men did challenge Henry VII after he was made the first Tudor king. John de la Pole led forces at Stoke in 1487, supposedly in favor of the imprisoned Edward of Warwick though it is just as likely that de la Pole was fighting for his own rights as Richard III's heir. He was killed, and Henry Tudor cemented his place in history as the father of the Tudor dynasty, a phenomenon that none of his forefathers could have predicted.
Henry also took the step of strengthening his claim through the blood of his wife. He married Elizabeth or York, the oldest child of Edward IV. She was a peaceful and uniting presence, bearing Henry sons to carry on the Tudor name. After more than three centuries, the Plantagenet dynasty was no more, and the Tudors would go on to become one of the most famous dynasties that ever reigned in England.