Loss of French land (such as Maine) brought on bouts of schiznophrinia that made him as useful as a vegtable. He couldn't even recognise his own son and heir.
This allowed for York to become the royal regant, he thought he would be incharge for 15 years, so when Henry came back and things went back to normal, he was unhappy with it.
1.2 Not a warrior King
Never knew his dad, who was such a warrior and took over alot of land in France. Henry was constantly compared to him - had no one to teach him how to be King
This made Henry a weak King as he couldn't live up to hs dad's high reputation and
1.3 Couldn't deal with the nobles
He mishandled the rivalry York and Somerset. Also his nobles didn't like Margaret of Anjou (York and Norfolk) meddling in state affairs as well as her closeness with Suffolk.
This lead to bitter rivalries in court, this caused the outbreak of fighting as the nobles would raise armies to fight with each other but the rivalry between York and Margert became apparent when they both fought for the regency/Protectorship of the crown during Henry's boys of mental illness.
2 Ovemighty nobles
2.1 Had his favorites
Sulfolk/ Somerset (the peace fraction) these gained most of the Kings patronidges.
Somerset becoming Captin of Calis - overthrowing York (becomes Luetnete of Ireland).
This angered certin nobles (York) as they fely unapresiated in court and there views weren't hearded.
2.2 Different Fractions in court
Peace Fraction = wants to appease France.
War Fraction = wants war with France.
This divded Henry's court as neither side could agree on what to do in France and Henry had a weak personalityit meant that nothing got decided.
Pariment of Devils declared the Yorkist rebels so they got there land confiscated.
3 Actions of the nobles
3.1 Over ruled the king
Sulfolks execution and getting of the treason charge.
York usurped Henry's heir in the Act of Accord, 1460.
3.2 Cades Rebellion
Was a popular uprising against the heavy taxes.
The ordinary people didn't support the King so they were willing to rebel.
3.3 Could quickly raise armies
When York/ Warwick joined fources they quickly raised an army of over 120,000 men which out weighted the Kings at the 1st Battle of St Albans.
Also for the Yorkist invasion they got 2000 Calais veterans on there side.
In both of these cases York managed to gain more power (after St Albans York became the principle advisor and he became the official heir to the throne from the Yorkist Invasion) this show that Yorks ambition was the major cause for the outbreak of fighting.