Former Trump defense chief Chris Miller warns Ukraine crisis could become World War III

Trump administration acting Secretary of Defense Chris Miller on Wednesday applauded Ukraine for executing what may be the "most successful military campaign" in history, but he warned that if the West does not "stand up" against Russian President Vladimir Putin, World War Three III could start — if it hasn't already.

"I fear if we don't get our act together ... this will be World War III," Miller said, adding, "Many people think it already is."

The Kremlin threatened to take nuclear measures last week after Sweden and Finland said they wanted to join NATO. The war has publicly turned bloodier, with Russia being accused of committing numerous war crimes in Ukraine.

"If we don't stand up right now and fight back against Putin, it's gonna get a lot worse," Miller told "Just the News, Not Noise."

Putin has denied accusations of committing "genocide," but Miller said the world needs to learn from history.

"We could kind of turn the other cheek for a while, but at the end of the day, we're gonna have to stand up to this guy more forcefully," he said.

The United States and much of the world have imposed numerous sanctions on Russia since the invasion of Ukraine began, while Putin remains undeterred.

Miller said he has directly recognized Ukrainian leaders for their military strength against Russia.

"When I was talking to the Ukrainian leadership, I had to remind them that they've executed the most successful military campaign in modern military history, if not forever, in military history," he told show cohosts John Solomon and Amanda Head.

"I think Putin seriously underestimated the will and spirit of Ukrainian people," Miller said. "And if anything, it's even more profound than it was before."

He said one of his biggest takeaways from visiting Kyiv is that Ukrainian leaders told him: "We'll do the fight. We just need the weapons and the equipment." 

Miller stressed that the Ukrainian military needs more supplies to fight Russia.

The former Trump administration defense chief said that Kyiv authorities told him they are worried the world will "forget" about Ukraine. 

He said that Ukraine's guerrilla warfare and power given the equipment they have will set an example for future battles.

"It's just not all about these mega-expensive weapon systems," he said. "It really comes down to these unmanned aerial vehicles and these rocket systems."

Some military experts believe that Putin has already lost the war in Ukraine as Russian troops are "regrouping" in the Donbas region.