France and England 1330-1350
In 1330 Édouard Ier had just taken control of its second kingdom. But France left way too much power for nobles, and given Édouard's English origins, as well as his being the King of England, nobles would every four or five years go on a revolt.
However, Édouard had an advantage over the previous French kings in handling the nobles : Aquitaine and its large revenues had become part of the French Royal Estates, as well as Champagne, which had great fairs. Thus he could ask for limited war taxes and ensure every peasant paid his taxes, so as to deal with nobles.
Among nobles, the most troublesome family was the Valois family. Not only did they have quite large estates and corresponding debt, but they also had a claim on the crown they would push despite having their sister maried to the King. They were thus the rallying point of the nobles' rebellions. They wouldn't remove their claim on the crown even when offered the County of Burgondy.
However, France was also undergoing a series of bad harvests from 1343 onwards, and the population, which was already too large for the country to feed, started starving and rebelling too. By 1345, the combination of both had cornered Édouard Ier. If he didn't manage to gain a large amount of prestige, he would have to bring troops from England - which would cost him his throne on the long term.
The Flanders were less troublesome, as most of their riches came from trading with England; and were them to stop paying taxes, Edward could confiscate land as French King and start an embargo as King of England.
Meanwhile, England was still in turmoil : the Anglo-Scottish war had started anew, and Edward Baillol had temporarily regained the throne on its own. The Scottish question remained a troublesome one for England as military intervention in Scottish affairs could bring on the great rebellion in France, while the lack of intervention couldn't help. Only a diplomatic success could help.
Or so he thought. Hardly had Edward Baillol been ousted from the Scottish throne, that Scotland declared war on England. It allowed England to attack Scots without giving the French Nobles the possibility to call their king a warmongerer and an usurpator. The Scots and the English clashed near Newcastle-upon-Tyne, killing half the Scottish army and capturing the rest. Meanwhile, to show its support for the war - and through massive amounts of money - Louis IV, Emperor of the HRE, made him general vicar of the HRE.
Although he intended to conquer all Scotland, Edward III of England could not as doing so would leave Scotland in the same state as France. The inconclusive Treaty of Leicester simply allowed him to restore peace - by gaining land enough to push frontiers to OTL, and a large amount of money.
Although the battle of Newcastle had been a great success for England, Edward himself found out he hadn't really gained in prestige from it. When asked why he hadn't joined with his army, he said : "In increasing order of importance, the quality of my generals, the situation in France, and the English weather." There was only one thing left he could do : enlarge France, if possible in the South.