General John (rtd) Allen said there would be mass unrest among the military rank and file over the policies that he would implement and pursue.
"I think we would be facing a civil military crisis, the like of which we've not seen in this country before," he said.
Allen, who served as commander of the International Security Assistance Force in Afghanistan, was a featured speaker at the Democratic National Convention. Later, Trump has called him a failed general.
"He (Trump) has got no credibility. In that regard, there has been progress with respect to the war against ISIS. We knew it was going to be a tough fight. But I don't have to justify myself to him," Allen said.
"What we do have to do is listen to what he's been saying about our military. He's called it a disaster. He says our military can't win anymore. That's a direct insult to every single man and woman who's wearing the uniform today," he said.
