In his farewell speech on Thursday, outgoing NATO chief Jens Stoltenberg will reportedly warn both the United States and Europe against the dangers of "isolationism", especially as Donald Trump seeks a return to the White House.

"We have heard voices on both sides of the Atlantic calling for America and Europe to part ways," he plans to say during his address in Brussels, as reported by AFP.

"Focusing on short-sighted national interests over long-term cooperation will not serve us well. Isolationism will not keep anyone safe."

This caution comes as allies in Washington express concern that a Trump victory in November could weaken US commitment to NATO.

It is worth noting that Trump has unsettled European nations by suggesting that the US might cease protection for NATO allies that fail to meet defense spending commitments.

Stoltenberg is set to transition the leadership of the Western military alliance to former Dutch Prime Minister Mark Rutte on October 1 after a decade of being in charge.

During his tenure, he has overseen a significant increase in defense spending among European members, largely driven by pressure from Washington and the ongoing war in Ukraine.

As of now, 23 of NATO's 32 countries are on track to meet the alliance's 2014 target of spending two percent of their GDP on defense.

"The good news is that we have delivered on the pledge we made 10 years ago," Stoltenberg will say. "But the bad news is that this is no longer enough to keep us safe."

With the war in Ukraine entering its third year, Stoltenberg will emphasize the need for NATO allies to ensure that Kiev can negotiate "from a position of strength" when the time for talks arrives. "Any future peace deal must be backed by strong and sustained military support. Not just pieces of paper."

The big picture

In light of the war in Ukraine, NATO's relationship with Russia has been severed. In his upcoming speech, Stoltenberg will assert that the alliance must eventually re-engage in dialogue with Moscow on matters like arms control.

"We have to speak to our neighbors. However difficult it might be. But dialogue only works when it is backed by strong defenses," he is set to state.

He will also caution against prioritizing economic relations with rivals like Russia and China over security concerns, declaring, "Freedom is more valuable than free trade." Furthermore, Stoltenberg will remind NATO members that "protectionism against allies does not protect our security."

France has been at the forefront of advocating for Europe to develop its own defense industry rather than relying on US or British arms. Reflecting on his tenure, Stoltenberg will mention the painful fallout from the US-led withdrawal from Afghanistan, which allowed the Taliban to regain power.

"Military power has its limits. The purpose of any future military operation outside NATO territory must be clearly defined," he will say. "We need to be honest about what we can and cannot achieve."

"During my time as secretary general, the relevance of NATO has been questioned. The alliance has been described as divided, obsolete, braindead," Stoltenberg will state. "But the reality is that NATO is strong, united, and more important than ever."

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