World leaders couldn’t communicate across continents. In the US military, pilots would lose contact with armed drones over the Middle East. Smart bombs would become dumb. Missiles would sit immobile in their silos. The US could lose early warning of nuclear attacks for parts of the Earth.

“There’s incentive to take that away from us,” said Peter Singer, who advises the Defense Department on space threats and authored “Ghost Fleet: A Novel of the Next World War,” which runs through a scenario of space war. “And that means if there was conflict on Planet Earth, it would almost inherently start with some kind of conflict in space.”

America’s chief adversaries in space are familiar ones: Russia and China are extending above the atmosphere the competition and conflict already boiling down here on Earth — from Syria to Ukraine to the South China Sea to cyberspace.

China and Russia are taking aim at America in space with a dizzying array of weapons seemingly borrowed from science fiction. Russia has deployed what could be multiple kamikaze satellites such as “Kosmos 2499” — designed to sidle up to American satellites and then, if ordered, disable or destroy them. China has launched the “Shiyan” — equipped with a grappling arm that could snatch US satellites right out of orbit.

“We would absolutely be shocked if the US military were not on a war footing now based on what we see,” said Paul Graziani, CEO of the civilian satellite tracker AGI.

These are not experimental weapons of the future, but weapons of today, already operating from Near Earth Orbit, just 100 miles up and home of the International Space Station, to Medium Earth Orbit at 12,500 miles, where the GPS satellites fly, all the way up to 22,000 miles in Geostationary Orbit, home of the nation’s most sensitive military communications and nuclear early-warning satellites.

Hyten warned that adversaries will soon be able to threaten US satellites in every orbital regime.

“We have very good surveillance and intelligence capabilities, so we can see the threats that are being built,” said Hyten. “So we’re developing capabilities to defend ourselves. It’s really that simple.”

The US Air Force Space Command was created in 1982 when Earth’s orbit was less contested, and today has some 38,000 employees, an annual budget of nearly $8.9 billion, and 134 locations around the globe. The broader Pentagon space budget is $22 billion.

Among the units are the 50th Space Wing, a team of more than 8,000 people charged with monitoring US and foreign military satellites. For now, these space warriors are little more than spectators, watching and observing this new space battlefield with no ability to fire back.

In 2015, Deputy Defense Secretary Robert Work expressed his grave concern that the military was not “ready to do space operations in a conflict that extends into space.”

He was proven right when, months later, US space forces were overwhelmed in a mock attack on US military satellites.

So many took notice when, in April this year, Work vowed that the US would “strike back” if attacked in space — strike back, he added, and “knock them out.”

“From the very beginning, if someone starts going after our space constellation, we’re going to go after the capabilities that would prevent them from doing that,” Work told CNN. “Let me just say that — having the capability to shoot the torpedo would be a good thing to have in our quiver.”

Work suggested a space equivalent of the depth charges US Navy warships dropped into the sea during World War II, setting off enormous explosions to fight off attack submarines.

“These satellites were built 15 years ago and launched during an era when space was a benign environment. There was no threat,” said Lt. Gen. David Buck, Commander of the Joint Functional Component Command for Space. “Can you imagine building a refueler aircraft, or a jet for that matter, with no inherent defensive capabilities? So our satellites are at risk, and our ground infrastructure is at risk. And we’re working hard to make sure that we can protect and defend them.”

So far, such weapons remain in the conceptual category. But the US is quietly developing advanced capabilities that could, some day, have defensive or offensive missions in space.

These include the US Navy’s Laser Weapons System, or LAWs, the US military’s first operational laser weapon now deployed in the Persian Gulf on board the USS Ponce. The X-37b, a pilotless space drone resembling the space shuttle without windows or a cockpit, has already flown multiple missions to space and has space watchers and US adversaries wondering if it could be used as a weapon.

Still, as Russia and China make rapid advances, some of the most senior military commanders are sounding the alarm that this is a war — the next world war and the first to extend beyond the confines of Earth — that America could lose.

“We’d be silly to say it’s not a possibility,” said Singer. “What any defense (planner) will tell you is, don’t look for the ideal outcome, plan for the worst day so that you can survive.”

Winning a space war means rethinking how the US wages war, and that rethinking is one our current military leaders and politicians are only just beginning to undertake.

So is the US moving quickly enough to respond to the new threats in space?

“I would say the answer was no,” said Gen. William Shelton, former head of Space Command. “Could we provide active defense of our own satellites? The answer’s no.”

The stakes couldn’t be higher. How the US responds to this new threat could determine who wins the defining conflict of the 21st century.