The United States successfully rallied the North Atlantic Treaty Organization coalition to non-member ally Ukraine's aid after being invaded by Russia, but the teetering global economy presents a new challenge for allied resolve, former CENTCOM Commander Gen. David Petraeus told "Life, Liberty & Levin."

Petraeus, who also served as CIA director, said it is in the West's interest to support Ukraine, adding that prior to the conflict, the United States and NATO were able to turn relevant Finnish intelligence data into "publicly releasable information." 

Finland, though not a NATO ally, has sought membership, for which the German Bundesrat became the latest federal legislature in the 30-member alliance to ratify.

"We have been working on training the Ukrainians through multiple administrations since 2014 and the occupation of Crimea and the areas of the Donbas by Russian-supported separatists," Petraeus continued. "You could argue that there are some things that we could have done earlier, and I might make that argument."

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Gen. David Petraeus, the new commander of U.S. and NATO forces in Afghanistan, speaks during a ceremony in which he formally assumed the command, Sunday, July 4, 2010 in Kabul, Afghanistan. (AP Photo/Dusan Vranic)

Gen. David Petraeus speaks during a ceremony in which he formally assumed the command in Kabul, Afghanistan. (AP)

"But the truth is, until the invasion took place, it was really hard to rally all of our European partners. It was also uncertain as to whether the Ukrainians were truly going to fight. One never does know."

Petraeus added he visited Ukraine shortly after President Volodymyr Zelenskyy's election and recognized the advancements its military had made, so he had little doubt of the nation's ability to fight.

He added that the key to a resolute alliance is economic stability in the member nations supporting Ukraine.

"There are fragile governments in Europe. Natural gas prices have skyrocketed. Their electricity costs will follow. That will be more challenging in terms of gasoline prices, inflation, economies will slow down and so forth," he said, as major members like Germany had relied on now-opponent Russia for their energy resources.

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NATO

NATO Secretary-General Jens Stoltenberg and members. (AP Photo/Bernat Armangue)

Former President Donald Trump famously gifted then-Chancellor Angela Merkel a white flag, which he said was a sign of her administration's "surrender" to Russia in forging a pipeline pact.

President Biden, meanwhile, has been under fire for largely halting advancements in American energy production, which Republican opponents say could be used not just to assuage U.S. economic strife, but to fill the hole left by NATO members' curtailment of Russian supply.

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"The challenge is going to be to keep the coalition together, keep the alliance steadfast in pushing back and in supporting Ukraine in every way that we possibly can," Petraeus said in the Sunday interview.

"We have to be in this now, I think, as a marathon, not a sprint. This could continue well through the summer and into the fall and winter, and it's in everyone's interest to try to stop the Russians as quickly as is possible."