England in mid-1483 was an unstable and dangerous place. The King, Edward IV, had died, and turmoil raged as to who was to be his sons, King Edward V's Protector and rule as Regent until the King was old enough to rule by himself. Richard Plantagenet, Duke of Gloucester and Uncle to Edward V, became a contender for this right and eventually surpassed this ambition to rule as Regent and instead became King in his own right. There are several different reasons as to why Gloucester made himself King after his brothers death and in this essay I will explore them.
Edward IV had married Elizabeth Woodville a 15 years before he died and many disapproved of the marriage; considering the Woodvilles a large, common family which were nothing but a drain on resources. They were given large swathes of land and power during Edward's reign and came to be one of the most powerful Yorkist families. The Woodvilles were Parvenu and many of the established nobility, including Gloucester distrusted and ultimately didn't like the Woodvilles.
As we have previously seen with Kings such as Henry VI, when a minor is born into power faction was guaranteed to ensue between those who wanted to rule. The new King Edward V was being tutored by Earl Rivers, the Queen's brother- he was a Woodville. Due to their power and standings with the new and previous King the Woodvilles were a threat to Gloucester. Gloucester didn't want them to be in control for the reasons I talked of earlier and in Stony Stratford on the 31st of April 1483, Gloucester and his ally Buckingham arrested Earl Rivers and his men as they attempted to transport Edward V to his coronation in London. His dislike of the Woodvilles was one of the reasons he made himself King- he could not allow a Parvenus family take what thought was rightfully his.
Another key reason is that Gloucester simply had the character and means to take such action- he was ruthless and