After the Tour de Nesle affair, because of it and the death of French Kings to come, the Royal house of Capet was in turmoil.
Following the death of King Philip IV of France on 29 November 1314, his eldest son became King Louis X. After the scandal with his wife who he had one daughter with, Louis X remarried to Clementia of Hungary in 1315. She was pregnant with their child when he died on 5 June 1316.
The question of female succession to the French throne was raised after Louis X death. He left only a daughter, Joan, and it wasn’t until Clementia gave birth to a son on 15 November 1316, John, who only lived and was “King” for five days. Furthermore, the paternity of his daughter was in question, as her mother, Margaret of Burgundy, had been exposed as an adulterer in the Tour de Nesle affair.
Louis X brother Philip, Count of Poitiers, positioned himself to take the crown, advancing the stance that the women should be ineligible to succeed to the French throne. Through his political sagacity he won over his adversaries and succeeded to the French throne as Philip V of France. By the same law he passed to get himself onto the throne, when he died on 3 January 1322, his daughters were denied the succession which then passed to his younger brother, Charles IV.
Like his brother before him, on 1 February 1328 Charles IV died leaving a daughter and a pregnant wife. If the unborn child was male, he would become King of France, if it was a girl, the choice of succession will be up to the nobles.
A girl ended up being born, therefore ending male line of the House of Capet.
By proximity of blood, the nearest male relative of Charles IV was his nephew, Edward III of England. Edward was the son of Isabella, the sister of Louis X, Philip V and Charles IV, but the question rose whether she should be able to transmit a right to inherit that she did not herself possess. I’m also guessing that they also didn’t want an English King on the throne of France, no matter who his mother is. The French nobility also balked at the prospect of being ruled by Isabella and her lover, Roger Mortimer, who were widely suspected of having murdered the previous English King and her husband, Edward II.
The assemblies of the French barons and prelates and the University of Paris decided that males who derive their right to inheritance through their mother should be excluded. Thus, the nearest heir through male ancestry was Isabella’s first cousin, Philip, Count of Valois, and it was decided that he should be crowned Philip VI of France. In 1340 the Avignon papacy confirmed that under Salic Law, males should not be able to inherit through their mothers.
Eventually, Edward III of England reluctantly recognised Philip VI and paid him homage for his French fiefs. He made concessions in Guyenne, but reserved the right to reclaim territories arbitrarily confiscated. After that, he expected to be left undisturbed while he made war on Scotland.