Fox News senior strategic analyst retired Gen. Jack Keane warned Friday that America's global adversaries have grown "more aggressive" because they see the U.S. as "vulnerable." Keane joined "Fox & Friends" to react to top military leaders from the the U.S. and China discussing Taiwan, stressing that Xi Jinping is sending an "unprecedented message" to President Biden. 

CHINA COMMITTEE CHAIR GALLAGHER PROPOSES TAIWAN DETERRENCE STRATEGY, DEMANDS PENTAGON CLASSIFIED BRIEFING

GEN. JACK KEANE: Yes, certainly both sides sort of accomplished what they wanted, a relaxation of tensions and certainly [military-to-military] talk is part of that. But what is coming out and my sources support it as well, is a rather profound and unprecedented message by President Xi to President Biden. And it had to do with the fact that the onus is on the United States if they want to avoid war over Taiwan. And President Xi told President Biden in some very direct language that the reality for him is that reunification with Taiwan is more important than maintaining the regional peace. And he expects the United States, if they want to avoid war, to support him in its peaceful reunification efforts. So he, I think, has taken a measure of the president similar to what Putin has done and similar to what the mullahs in Iran have done. And they see a vulnerability here and an ability also to take advantage of that vulnerability. And they also see in the United States a declining political will. And that is why our adversaries are more aggressive. We see with President Xi, we see with Putin and his invasion, we see it [with] Iran and its proxies in the Middle East. The reality is right in front of us, we've got to see the danger and wake up and start dealing with these adversaries

Biden speaking with Xi Jinping

Chinese President Xi Jinping and U.S. President Joe Biden take a walk after their talks in the Filoli Estate in the U.S. state of California, Nov. 15, 2023. (Photo by Li Xueren/Xinhua via Getty Images) ( Li Xueren/Xinhua via Getty Images)

Top-level U.S.-Chinese communications have been re-established after months of antagonism and pointed silence.

Joint Chiefs of Staff Chairman General Charles "CQ" Brown Jr. spoke Thursday morning with General Liu Zhenli — chief of the Joint Staff Department of the Central Military Commission in the People's Liberation Army.

"We've been clear about the importance of opening lines of military to military communications with the PRC at the senior-most levels. However, it's just one step, an important step, but it's not the last step," a senior U.S. official told Fox News of the call.

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The re-establishment of high-level communications follows a collapse in goodwill between the two nations after then-Speaker of the House Nancy Pelosi visited the island of Taiwan in August 2022.

China, which aggressively claims sovereignty over Taiwan despite the island's autonomous government, immediately ended a slew of diplomatic collaborations, including the types of phone calls re-established this week.

Fox News' Timothy H.J. Nerozzi and Liz Friden contributed to this report.