pope urban 2 wrote on Jun 5
th, 2008 at 11:08pm:
AND ALL MARRIED WOMAN ARE FORBIDDEN UNTO YOU, EXPCEPT THOSE CAPTIVES THAT YOUR RIGHT HAND POSSESES. IN REFERENCE TO THE JEWISH WOMAN HELD CAPTIVES AS SLAVES IN MEDINA, WHERE MOHAMMAD MURDERED THE JEWS WHO PREVIOUSLY HAD HELPED HIM.
They were treated according to their own laws. Let's examine Jewish law in this situation. The Banu Qurayza conspired against the Islamic State with the Pagans and fought against the state. They committed treason and engaged in battle against the Muslims. Jewish Law dictates the following:
Deutronomy 20:10-15
When you march up to attack a city, make its people an offer of peace. If they accept and open their gates, all the people in it shall be subject to forced labor and shall work for you. If they refuse to make peace and they engage you in battle, lay siege to that city.
When the LORD your God delivers it into your hand, put to the sword all the men in it. As for the women, the children, the livestock and everything else in the city, you may take these as plunder for yourselves. And you may use the plunder the LORD your God gives you from your enemies. This is how you are to treat all the cities that are at a distance from you and do not belong to the nations nearby.
Those Jews were dealt with according to their own laws. The difference is that Muhammad pbuh offered to spare the lives of any people who converted because by accepting Islam they would be free from sin and not liable to Jewish law.
Say what you want about that, but they were certainly not compelled to become Muslim. They committed a crime and were punished for it.