Retired Adm. James Stavridis, a former NATO supreme allied commander, on Wednesday defended the organization after comments by President Trump Donald John TrumpBiden on Trump's refusal to commit to peaceful transfer of power: 'What country are we in?' Romney: 'Unthinkable and unacceptable' to not commit to peaceful transition of power Two Louisville police officers shot amid Breonna Taylor grand jury protests MORE questioning why the U.S. must commit to defending all countries in the alliance.

Stavridis said on MSNBC that it’s important for the U.S. to uphold its end of the NATO agreement and help allied countries because those countries will, in turn, assist the U.S.

“They went with us to Iraq, to Libya, to the Balkans, to Afghanistan,” the former commander said of NATO countries.

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“I signed, sadly, thousands of letters of condolence to Europeans who died fighting because the United States had been attacked,” Stavridis said. “I think that’s a pretty good equation in terms of NATO.”

Stavridis’s comments were in response to Trump questioning why the U.S. should defend all NATO countries during an interview with Fox News’s Tucker Carlson that aired Tuesday.

"I've asked the same question," Trump replied after Carlson asked why should his "son go to Montenegro to defend it from attack?"

"Montenegro is a tiny country with very strong people,” Trump said. “They are very strong people. They are very aggressive people, they may get aggressive, and congratulations, you are in World War III.”

"I understand, but that's the way it was set up,” Trump continued. “Don't forget, I just got here a little more than a year and a half ago, but I took over the conversation three or four days ago and I said, 'you have to pay.' ”

Trump has repeatedly railed against NATO allies' slow efforts to meet defense spending goals. As he attended the NATO summit in Brussels last week, he demanded that alliance members spend at least 4 percent of their gross domestic product (GDP) on defense — a goal that not even the United States currently meets.

The U.S. spent 3.6 percent of its GDP on defense last year.

A number of NATO members have increased their defense spending, and several are set to meet the 2024 goal of spending at least 2 percent of their GDP on defense.