The last tribe remaining was the Banu Qurayza. Like the others, the Qurayza were a peaceful community of farmers and tradesmen who eventually surrendered to Muhammad without a fight. Although the prophet of Islam had been wise enough not to order the wholesale slaughter of the first two tribes following their defeat (which certainly would have stiffened the resistance of the Qurayza), there was no practical reason for Muhammad to repress his genocidal urges once the last tribe had surrendered their wealth and power.
Some 800 surrendered men and boys (and at least one woman) from the Qurayza tribe were beheaded by the prophet of Islam in a bloodbath that is of acute embarrassment to today’s Muslim apologists (according to Ibn Kathir, the number ranges from 400-900 v.3 p.170). It is an episode that is not only completely at odds with the idea that Islam is a peaceful religion, but also refutes the claim that it is the heir to Christianity, since even that religion’s most dedicated critics could hardly imagine Jesus and his disciples doing such a thing.