How strong was Henry VII's claim to the throne?

To understand the competing claims to the throne in the fifteenth century, we must trace back to Edward III, whose blood ran through many veins, G.R Elton would come to later argue that in fact, it ran through
 'too many'.

Although none of Edward III's became King's, the descendents of the four eventually did.

Henry Tudors claim was essentially weak, however his Mother was a descendant of Edward III's son, John of Gaunt and his mistress, therefore Margaret was illegitimate. However, John of Gaunt would eventually legitimise his bastard children, naming them 'Beaufort' after the castle they lived in.

Practice Question:

Explain why Henry Tudor was able to usurp the throne in 1485 (25 marks)