Politics played a huge role in Jehanne’s demise.
After her capture by the English, her fate was almost a foregone conclusion. Her declaration that she was sent by God to deliver the French from English occupation was simply unacceptable. The English essentially had to declare her a heretic. To accept that this peasant girl (who was outrageously overstepping her social station, by the way) was God’s messanger was admitting that they were wrong in occupying France. In a nutshell, if Jehanne was who she said she was, then the English were defying the Lord’s will, and that simply wasn’t something they were willing to accept.
Executing her for heresy was a simple way of taking care of a larger political problem. Generally, uneducated peasants like Jehanne were easy to trap into admission of heretical beliefs. Questions were cleverly worded so that any answer would be wrong. For example, the inquisitors asked her if she was in a state of grace. To say yes would be saying that she knew the mind of God-- blasphemy, and to say no would be to admit she was a sinner and a heretic. Jehanne’s answer was astonishing: “If I am, may God keep me there. If I am not, may He bring me to it.” For an illiterate, uneducated peasant girl, this was incredibly clever.
The gender issue was part of it-- after all, the clerics had strong, serious doubts that if God had anything to say about the war, he would have chosen a dirty peasant girl who couldn’t even write her own name without assistance, and not a bishop or lord. Not only was Jehanne overstepping her natural subserviant role as a woman, but she was also overstepping her social status.
Okay, they quietly admitted, she had done some apparently miraculous things, but it must have been because she was a witch, being fed information by the devil. According to a source, she knew of a buried sword beneath an altar which the priests of the church had no knowledge. She was also able to tell the dauphin of France a secret which convinced him that she was truly sent by God, though we do not know what it was. Some scholars speculate that she told him he truly was legitimate-- something about which there was some debate.
The issue of the clothes was simply a way of forcing the issue. Jehanne, threatened with being burned at the stake, “confessed”, and the Church was forced to accept her penitence. (The only people who could be legally burned were relapsed heretics-- meaning that they had been warned, and refused to change or went back to their old ways. Of course, the Church found ways around that.) Jehanne claimed that they promised after she repented that she would be sent to a convent to be imprisoned, instead of where she was currently housed. She agreed to dress again in women’s clothing.
Various sources hint that Jehanne was either raped or assaulted in some way which led her to resume wearing men’s clothing. (Which had been temptingly placed in her cell, apparently. Else, where would she have gotten them?) She had always claimed that she wore men’s clothing to protect her virginity. (Her hose were tightly laced to her doublet, meaning that they could not be removed without quite a bit of effort, rather than the easy access provided by a woman’s dress.)
Putting the men’s clothes on was the relapse that the Churchmen needed to finally be rid of her. One can almost hear their sigh or relief down through the ages. They’d finally done it: after a lengthy trial in which the impertinent little witch had outwitted them repeatedly, and then her dissapointing recantation, they finally had what they needed to kill her.
When all the chips fell, the king of France was not willing to take the risk in trying to get her back. The fact that she was on trial before the Church, even if the trial were grossly rigged, had weight. The uncertain king could not afford to appear to support a heretic, or to have his crown credited to a witch, no matter what secret she had revealed to him. Secondly, she was getting a lot of public adultation, and the king may have been jealous, and nervous that Jehanne’s power would soon be greater than his own. She had also outlived her usefulness. While she was winning, she was a wonderful thing to have at the head of the army-- she was a powerful mascot, so to speak. But once she started losing battles, it must have seemed like God’s blessings had been lifted from her.