A

"That Lord Valois, our brother, King of France,/
Because your highness hath been slack in homare,/
Hath Seized Normandy into his hands."
-Queen Isabella III, i, 62-64

This is a conflict that just seems so be oiling below the surface of the entire play. France has invaded England's holdings across the channel, yet Edward seems too wrapped up in his love for Gaveston to notice. He continually makes references to his lack of fear, since they will inevitably make peace with the French, but shouldn't this be his first priority? Shouldn't he, as King, put his nations safety first before his petty squabbles with various members of the court? Isn't that how empires fall? The same can be said, however for the nobles opposing the King. If, as they say, they care so much for the nations, for its people, shouldn't their first priority be put on a foreign invader who is threatening further annexations? It's absolutely ridiculous, the monarchy deserves to fall, and the nobles deserve to be executed and/or thrown in the Tower of London.
I think that it's interesting (and vaguely disappointing) that Gaveston's death occurs off stage. It is perhaps a choice made out of necessity (lack of funds to display a beheading on stage), but I have to think that it was an active choice on Marlowe's part to leave that scene out. I think that it portrays a desire to, in the end, show that Gaveston is not actually important to the conflict. Granted, he is the target of the conflict that currently rages in England, but what the nobles speak about more often is the King's obsession and preferential treatment towards him, not Gaveston himself. It's never, as far as I can remember outlined why he was exhiled by Edward I, and thus it is seemingly unimportant, all that matters is that he exists and is back, and the king really enjoys his company. So, when Gaveston dies, it is not show, instead you see the King being informed of it, and his reaction is the centerpiece of the play, not the execution itself.