>>15410657(pb)

>Hoping to make several attacks at once, the confederates persuaded the Muslim-allied Medinan Jews, Banu Qurayza, to attack the city from the south. However, Muhammad's diplomacy derailed the negotiations, and broke up the confederacy against him.

>As a consequence, the Muslim army besieged the area of the Banu Qurayza tribe, leading to their surrender.

Then the apostle went out to the market of Medina (which is still its market today) and dug trenches in it. Then he sent for them and struck off their heads in those trenches as they were brought out to him in batches. Among them was the enemy of Allah Huyayy ibn Akhtab and Kaab ibn Asad their chief. There were 600 or 700 in all, though some put the figure as high as 800 or 900. … Huyayy was brought out wearing a flowered robe in which he had made holes about the size of the finger-tips in every part so that it should not be taken from him as spoil, with his hands bound to his neck by a rope. When he saw the apostle he said, ‘By God, I do not repent of having opposed you, but he who forsakes God will be forsaken.’ Then he went to the men and said, ‘God’s command is right. A book and a decree, and massacre have been written against the Sons of Israel.’ Then he sat down and his head was struck off.

https://en.wikipedia.org/wiki/Battle_of_the_Trench#Reason_for_battle

It was also mostly due to some Meccan hate from the disbelievers to finish off the Muslims, as the prophet had given Makkah a new religion, Islam, which was meddling with the old ways, Idol Worship, and challenging with the authority of the elderly that held Makkah in a dictatorship.