How did the magana carta and the model of the parliament contribute to the decline of feudalism?

By strengthening royal authority at expenses of nobles and shifting power to common people.

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This is true for the Magna Carta, but not the same for the Model Parliament introduced by Edward I. The Parliament gave a voice to both common people AND lords. Both of them had voices and it didn't really weaken feudalism, as both sides of the story benefited from this. WIN-WIN situation.