Officials who have held America’s top national security positions tell "Axios on HBO" that the nation has never before faced such a tangled web of threats — and they worry about the government's capacity to confront them.

• David Petraeus, former CIA director and retired four-star general, and H.R. McMaster, former national security adviser, both name the rivalries with Russia and China as the greatest threats of our time.
• Janet Napolitano, former Homeland Security secretary, lists climate change, cyberattacks and gun violence.
• Leon Panetta, former CIA director and Defense secretary, is most concerned about cyber threats.
• Lisa Monaco, former White House homeland security adviser, says her biggest fear is a deadly pandemic.

The big picture: The last time the global threat picture was this crowded and combustible was in the lead-up to World War I, Panetta says.

• Between the lines ... Some of the threats are familiar: Russia, nukes, terrorism. But many are exacerbated by new technologies — from AI-powered weapons to viral hatred on social media — and by climate change.

Security officials increasingly view Russia and China — separately and together — as a threat to U.S. security.

Between the lines: “What I consider two of our strongest adversaries are now working together to try to undermine stability in the United States of America,” Panetta says. “This is not like dealing with some kind of rogue nation."

• “They have great cyber capabilities. They have capabilities in space and on missiles. They both have very strong military capabilities," Panetta tells "Axios on HBO." (See a clip.)
• “Their cooperation ... is a very dangerous moment for the United States of America.”

Zoom out: Russia and China aren’t formal allies but they are de facto allies.

• They share about 2,600 miles in border.
• Chinese President Xi Jinping and Russian President Vladimir Putin have emphasized their newfound cooperation through steps trivial (flipping pancakes together) and substantial (joint military exercises and a linked oil-and-gas system).
• As both McMaster and Petraeus point out, both countries have suffered serious economic blows from U.S. sanctions and tariffs.

Our thought bubble, per future editor Steve LeVine: Smart U.S. policy will attempt to create discord between Russia and China through carrot and stick.

• A major blunder would be pushing too hard with financial punishments, and incentivizing Moscow and Beijing to bypass the U.S. trade and monetary order.
• When the dollar's primacy materially dwindles, that will be game over in balance of power with the East.

Two of the countries where the threat of direct military conflict with the U.S. is greatest are Iran and North Korea.

Threat level: H.R. McMaster, who until last April was involved in the most sensitive discussions on those countries with President Trump, warns it’s “difficult to overstate the threat from a nuclear North Korea.”

The big picture: McMaster argues North Korea could directly threaten “the United States, China, Japan, the world” with its nuclear arsenal and could also engage in “nuclear blackmail.”

• McMaster also points to the risk of wider nuclear proliferation in Japan, South Korea and beyond, asking: “If North Korea gets a weapon, who doesn’t?”

Meanwhile, the administration has focused its ire on Tehran.

• McMaster places Iran on the list of the greatest global threats because of its support for groups the U.S. has designated as violent proxies and terror groups.
• His successor as national security adviser, John Bolton, has increased the pressure on Iran further still, warning of "unrelenting force" if Iran or its proxies strike U.S. interests.
• That has led to a fear that tensions could spill over into military conflict, even though Trump and Iranian leaders have both said they don't want a war.

A new era where weapons of war are becoming more intelligent and more enabled by data — such as unmanned ships, submarines or drones — raises complex challenges for national and global security.

• Threat level: If technology is allowed "to start making big decisions on its own ... we might be doomed by technological advances," David Petraeus tells "Axios on HBO."

Driving the news: Experts are grappling with the ethics of developing autonomous weapons, which suggest the possibility of a computer deciding on its own to take human life.

• UN Secretary-General António Guterres has urged AI experts to ban autonomous weapons, calling them “morally repugnant.”
• Drones — low profile and easily preprogrammed with GPS routes — are just the beginning of warfare with AI. Recently, a drone blast killed several people in Yemen, including the Yemeni government's head of military intelligence.

Fully autonomous weapons don't exist today.

• But Petraeus warns even a world of semi-autonomous weapons could create a frightening future for humankind.

Our thought bubble, from Axios AI reporter Kaveh Waddell: The big challenge now is to slow the world’s slide toward an automated weapons race fueled by mutual distrust and a lack of information.

• As international efforts to ban autonomous weapons stall — in part thanks to the U.S. — look for the Pentagon to update its policies on automation late this year.

Go deeper: The AI arms race is a self-fulfilling prophecy

Another global threat — one that is a repeated refrain amongst the White House, Centers for Disease Control, former national security advisers and even Bill Gates — is a pandemic.

Between the lines: Influenza is of particular concern for health officials, even though there are more contagious viruses — for example, measles — and more deadly ones, like Ebola.

• But the flu virus can mutate quickly, sometimes acquiring a new ability to infect humans easily, causing concern about its potential to spark a pandemic, which happens when a new strain appears that most have no immunity against.

"The combination of a new deadly strain of flu plus air travel plus the ease with which it can be transmitted to other people. That really is the worst case scenario."

Our thought bubble, from Axios' Eileen Drage O'Reilly: Emerging virulent pathogens are a threat each nation needs to report on a transparent basis to promote possible global coordination to halt their spread.

Mass gun violence is one of the top threats to safety and security in America, Janet Napolitano tells "Axios on HBO."

What's happening: The U.S. has more mass shootings than any other country in the world.

• Napolitano notes that federal resources are steered toward shootings motivated by “terrorist ideology,” but most are simply treated as “a local crime, a state crime.”
• Even in cases where suspects have been radicalized, they're difficult to identify in part because there's often no broader conspiracy to uncover.

Our thought bubble, per Axios' Stef Kight: There is a generation of young people with little memory of foreign terrorist attacks such as 9/11, but who have grown up witnessing their peers killed by domestic terrorists. These young people will soon be voters.

Go deeper:

• Three decades of school shootings
• The deadliest mass shootings in modern U.S. history
• Second Parkland shooting survivor commits suicide