John of Gaunt now had defeated most of Richards main allies in the south, but the campaign had exhausted the men. Rather then risk an assault on London, Gaunt wanted to strike a blow and establish a southern base of operations for the next year. Oxford became his next target, controlled by the aging Earl of Oxford, Aubrey de Vere, Gaunt laid siege.
Oxford though did not want to go without a fight, and managed to resist the invaders until September. Gaunt realised that his position could become unstuck if he moved at this stage of the season, so he awaited news of his Percy allies from the north and their progress moving south. This delay has been cited as one of the reasons for the defeat of the Lancastrian Army, but any attempt to attack London after the battle of Curbridge would have undoubtedly resulted in defeat.
When news reached Gaunt of the Defeat of his allies at the hands of the Earl of Norwich, Gaunt knew that he would need to move on Richard in London as soon as the campaign season started the next year, it would be a do or die attack.
Richard for his part wasn't idle in his capital whilst his generals men fought and died in his name in the country, feverishly working in France he managed to use his connections with the slightly less anti-English Burgundian faction in the French court. This faction wanted a written treatise on the 28 year truce that Richard managed to secure with his betrothal to the princess Isabelle de Valois a few years previous. Richard agreed to the terms, in return for men and arms to crush the Gaunt rebellion, England would sign a treaty to protect the tenuous peace between the nations.
In secret though, Richard agreed to support Burgundy in their feud with the Duke of Orleans faction within the French court of the 'Mad King'. This would have repercussions later in Richards reign.
As 1399 rolled around Richard had secured the support and was raising his main army in London, spurred on by the French reinforcements and a renewed sense of hope after the delay at Oxford.
Gaunt left Oxford with a token garrison in February, hoping to catch Richard unready for the early start in the unseasonably warm late Winter of 1399. Gaunt had received some extra men from Lancashire, and some of the remnants of the Percy force that had managed to get south over the Winter. Richard managed to ready his men though, and moved to meet him in the Oxfordshire countryside.
Gaunt had to move north to avoid the castle at Wallingford, and to try and circumvent some of Richards forces who were closing in, but it failed as Richard simply cut them off before they could manoeuvre around them.
The battle was joined near Woodstock, Oxfordshire, this was poignant as it was the birthplace of Edward, 'the Black Prince', father to Richard and brother to Gaunt. The battle was the largest to be fought in England for generations, as both sides clashed, both Richard and Gaunt personally led their sides to the battle.
The battle was fierce, and bloody, Gaunt's centre was decimated and crumbled, whilst his cavalry succumbed to the French Allies Richard had brought. Longbowmen featured less then many other battles as Gaunt had left many in Oxford to protect it, whilst Richard had a reduced force due to a fire at the Royal Armoury containing most of the Longbows stored for the coming campaign. So it was that crossbows played the biggest part in any battle that they had on English soil and the French Archers, and French trained Englishmen did reasonable damage to the Cavalry, being more of a quirk of history rather then a decider in the battle.
In the end the battle was almost a draw, with both sides with mounting casualties. By the end of the day, the feast of St Oswald (the 28th of February) both sides pulled back. Even though the battle wasn't a defeat for Gaunt, the opportunity to take Richard and London, and therefore the Crown, was gone.
The morning after Gaunt learnt that a force under a renewed Le Despenser managed to take Oxford from Gaunt's meagre garrison. Faced with destruction in all other directions, Gaunt was left with no choice but a long march back to Lancaster.
But even that was soon unavailable as John Holland, constable of Cheshire had raised a force and moved to block Gaunts route back to his home county, in the Battle of Malkins Bank, Gaunt's beleaguered and battered army was finally fully defeated in what was the end of the Plantagenet Civil War. Gaunt was captured and spent the rest of his time in the Tower, dying later that year in his sleep from natural causes.
With the death of Gaunt and the main threats to Richard gone, the Plantagenet Civil war was over, actual casualty numbers vary wildly, from a low 8,000 estimate, to 30,000, which is calculated including several outbreaks of dysentery on the passing armies of the time.
The Civil war is a tale of What if's: What if the Percy's hadn't been defeated by Norwich?, what if Oxford had been taken quicker?, what if Gaunt had 'rescued' Henry from the Montacutes?