The Angers Agreement of July 1470 saw the forging of an unlikely alliance between Richard Neville, earl of Warwick and Margaret of Anjou and paved the way for the short-lived 'readeption government' of Henry VI.
After the great Yorkist victory at Towton in 1461 Henry VI and Margaret of Anjou spent the next few years attempting to hold onto a small Lancastrian enclave in the north of England but after a series of setbacks Queen Margaret and Prince Edward went into exile in France in August 1463. Henry VI held on to a small enclave for a little longer but was forced into hiding after his last field army was defeated at Hexham in 15 May 1464. The fugitive king was captured in 1465 and was kept a prisoner in the Tower of London. He remained alive because he was a less impressive figurehead for Lancastrian resistance than his young son Edward, who would also have gained a great deal of sympathy if his father had been killed.
During the 1460s Warwick and Edward IV grew apart. Warwick expected to be the power behind the throne, but Edward soon proved that he wouldn't accept that. Warwick was still richly rewarded by the king, and was the second most important man in the kingdom, but he had to share his power with other councillors, and in particular the Woodville family, relatives of Edward's queen, Elizabeth Woodville. The two men also argued over foreign policy, with Warwick supporting a French alliance and Edward favouring an alliance with Burgundy and Brittany against France. By 1469 Warwick had decided to use force to take control of Edward's government. His first attempt was a temporary success, but his second attempt, early in 1470, failed after his allies were defeated at 'Losecote Field' (12 March 1470). Warwick failed to convince Lord Stanley to help him, and then fled south. He gained a fleet at Dartmouth, and sailed east along the English Channel. An attempt to seize his old flagship at Southampton failed, and much to his shock he was refused access to his stronghold at Calais, where he had been captain since the 1450s. After a brief naval campaign in the Channel Warwick was forced to seek refuge in France, arriving at Honfleur in the Seine in May 1470.
Louis XI of France decided to arrange for a reconciliation between Warwick and his bitter enemy Margaret of Anjou. Louis hoped that a Lancastrian England dominated by Warwick would ally with France, allowing him to concentrate his efforts on gaining control of Brittany and Burgundy. Both parties probably saw this agreement as their best chance of success. Warwick had been expelled from England and repulsed at Calais, the base he had used with great success in 1459-60. Queen Margaret had watched Edward IV establish himself apparently firmly on the throne from her exile in France. Her husband was in prison in the Tower and their son Prince Edward was growing up away from his kingdom.
On 22 July 1470 Warwick and Queen Margaret met at Angers Cathedral. Margaret forced Warwick to spent twenty minutes on his knees in front of her before she pardoned him for his past misdeeds. The two sides then came to a formal agreement (presumably the details had already been agreed before this public act of political theatre).
Warwick agreed to invade England and restore Henry VI to power. Jasper Tudor would accompany him as the Lancastrian representative. Only once it was safe would Queen Margaret and Prince Edward travel to England.
In return Warwick's younger daughter Anne would marry Prince Edward. The young couple were officially betrothed on 25 July in Angers Cathedral, and would be married in December 1470, at which point their cause looked very healthy - Warwick's invasion had succeeded, Henry was back on his throne and Edward IV was in exile in Flanders. Warwick's ally in his revolts, Edward's brother George, duke of Clarence, was to become Duke of York (replacing his brother). He was also acknowledged as heir to the throne if the Lancastrian dynasty failed, although that did put him behind Prince Edward, any heirs he might produce and presumably the Beauforts.
At first everything went well for the participants in the Angers Agreement. Warwick returned to England in September 1470 with French support. His brother John Neville, Marquess Montagu, finally turned on Edward IV and in October Edward was forced into exile. Henry VI was returned to the throne, beginning his brief 'readeption' government.
However the new regime had weaknesses from the start. Warwick needed to reconcile the Yorkist establishment, which had largely survived Edward IV's fall intact, with returning Lancastrians who would expect the return of their lands and titles. Henry VI was an unimpressive figurehead and the young Prince Edward, who might have been a good figurehead for the cause, remained in France for far too long. Edward refused to accept his exile, and in the spring of 1471 he landed on the Yorkshire coast. Warwick and his supporters bungled the early stages of the campaign Edward, who was able to reach London ahead of them. He then turned back and defeated and killed Warwick at Barnet (14 April 1471). On the very same day Queen Margaret and Prince Edward landed in the south-west. They were able raise a sizable army, but the resulting campaign ended in catastrophe at Tewkesbury (4 May 1471). Prince Edward was killed in the battle and soon afterwards Henry VI was murdered in the Tower. The main line of the Lancastrian dynasty had been eliminated and Edward IV was secure on his throne for the rest of his life.