Re: Banu Qurayza
The OPs take on history is confused, and it's unclear if she is pro-kaffir (to the extent that she wished the early Muslims would have been slaughtered), or simply disturbed over the alleged (emphasis on alleged) conclusion to the betrayal of the Muslims by the BQ.
First, the muslim arrival in Medina was precisely so they could intermediate (i.e. "interfere") in the affairs of the locals. The Prophet (pbuh) was brought in to bring peace to the already warring tribes, and did so through the pact of medina. All present were signatories to the pact, and none disagreed to any of the terms at that point in time. After the pact was created, all were beholden to it, and the Muslims ceased to be migrants but citizens of Medina proper. So, migrating again in the face of treachery was uncalled for. Turning the other cheek would have meant the neck of the Muslims. This wasn't some stupid treaty...such a suggestion is moronic. It was the key for peace, and it was others within Medina that sided with the war mongering Quraysh in clear violation of the treaty that had anything but peace on their minds.
Second, the policy of exile was a failure. The Banu Nadir began agitation against the Muslims, in clear violation of the pact, with those who wanted the Muslims dead and gone. The chief of the tribe was executed, so his tribe could be spared. Nonetheless, it seems the policy of supporting the Quraysh at the expense of the Muslims was a tribal matter, and not the whims of the former chief. The exposed plot to assassinate the prophet (which the OP flippantly refers to as a self-revealed prophecy...the attempt was neither denied and alternative sources suggest it was a tip off and not revelation), was the last straw...the Banu Nadir were exiled for their continuous violation of the pact. THey returned with 10,000 men surrounding 3000 Muslims in what would end with the battle of the Trench.
The BQ, rather than at the very least stay neutral (the pact seems to imply they were obligated to come to the defence of Muslims), entered into talks with the Meccans. That these talks broke down was not a sign of their good will or their honourable intentions. They were simply looking out for their own interests, and were biding time until the Muslims were defeated and dead.
The Banu Nadir couldn't keep to the terms of the pact of Medina, nor the terms of their exile...it was clear that these facts weighed on the mind of Sa'ad.
The OP suggests that the battle was for booty. 10,000 men against 3000...and booty was a certainty? Such lunacy can't be taken seriously.
The OP suggests that by letting the BQ go, they would then support him. This is unreasonable, and given the battle that was just concluded, unlikely.
The OP asks why the Propeht (pbuh) feared being attacked or killed...asinine assertion given that he was present at every battle. Second, any action done to him would no doubt repeated on the entire Ummah...his mission was to establish an Ummah, not to be some hippie hanging out in the dessert.
The OP suggests that if it were a "true" religion it would have spread anyway...the fact it is, these battles did little to spread Islam, and it takes the cake to suggest that this was the intent of any of them. They were fought to protect and secure those who were Muslims and threatened with elimination because of it. The idea that Muslims really didn't need to do anything, and God would have protected Muslims anyway is a bit much. One of the underlying themes of Islamic history is that the establishment of the Ummah was so the faith could survive after the last prophet...in the end that meant hard choices, difficult politics, and fighting. There would be no more prophets delivering faithful men from evil people. With this, it becomes obvious why it made sense for the Muslims to take arms and not sit around waiting for a miracle...or slaughter.
The OP suggests it was not religious but political. Yes. It was. But did the prophet (pbuh) have the "power" to stop it? For what purpose?
The OP suggests that these events somehow motivate the Taliban. The question is: how? No parallels exist.