Henry VI refused to give up his claim to the French throne (in 1415 at the Battle of Agincourt, Henry V was made heir to the throne after having great military success).
Suffolk negotiated the marriage of the French King's niece - Margaret of Anjou - to Henry VI.
Suffolk secretly agreed to hand over Anjou and Maine to France.
1447: York was sent to Ireland
Henry VI and Suffolk saw the Duke of York as a potential threat.
To rid England of York, after his return from France in 1445, York was dispatched to Ireland in 1447 as the new appointed Lieutenant of Ireland.
1447: The death of Gloucester
Henry VI thought that Gloucester was going to overthrow him. In Feb 1447 - arrested, imprisoned - mysteriously died.
York is heir-presumptive (Henry VI had no child to be heir).