LONDON — Hot on the heels of last week's NATO summit that highlighted the threat and "systemic challenges" posed by Russia, China, North Korea and Iran, geopolitical and defense experts say the West must now prepare itself to confront such adversaries.

Former NATO chief George Robertson on Tuesday warned that the U.K.'s armed forces must have the capacity to confront a "deadly quartet" of rivals, as he launched a strategic review into Britain's defensive capabilities.

"We're confronted by a deadly quartet of nations increasingly working together," he said, in comments reported by Sky News.

"We in this country and the NATO alliance … have got to be able to confront that particular quartet as well as the other problems that are pervading the world," he added.

Robertson did not explicitly name the members of the quartet, but the other three countries are thought to be Russia, Iran and North Korea — countries that NATO last week described as posing a threat and systemic challenges to "Euro-Atlantic security."

The use of the word "deadly" to allude to China matches a ramping-up of rhetoric against Russia's ally in last week's NATO summit, where Beijing's status as an adversary was acknowledged more publicly than ever.

In the summit declaration, China was described as a "decisive enabler" of Russia's war against Ukraine and as posing "systemic challenges to Euro-Atlantic security," with the military coalition citing "sustained malicious cyber and hybrid activities" and concerns over the diversification of Beijing's nuclear arsenal and space capabilities.

NATO leaders meeting in Washington agreed that China's "coercive" policies and ambitions challenged the defense pact's "interests, security and values," positioning Beijing as a key opponent of the alliance.

The NATO declaration also said China's "deepening strategic partnership" with Russia was of "profound" concern, although it was clear that Russia and its ongoing war on Ukraine remained the alliance's most immediate concern.

The coalition described Moscow as having "shattered" peace and stability in the West and having "gravely undermined global security." Russia's nuclear capabilities and hybrid action through proxies, such as malicious cyber activities, provocations at allied borders and disinformation campaigns were all noted as particular threats.

Russia's allies North Korea and Iran were also accused of "fuelling Russia's war of aggression" against Ukraine by providing direct military support to Russia, such as munitions and unmanned aerial vehicles (UAVs), which, NATO said, "seriously impacts Euro-Atlantic security and undermines the global non-proliferation regime." 

Russia and North Korea deny arms transfers have taken place. Iran has previously said it supplied drones to Russia, but claimed it had shipped these before the war started. China has been threatened with sanctions after being accused of sending "dual-use" materials, including weapons components and equipment, for Russia's defense sector to use in its own weapons' production. 

China denies supplying weapons to Russia, with Chinese foreign ministry spokesperson Lin Jian reportedly describing the latest NATO comments as "biased, slanderous, and provocative." He also dismissed NATO as a "relic of the Cold War." China's mission to the European Union said that the NATO statement was "filled with Cold War mentality and belligerent rhetoric."

Ian Bremmer, founder and president of Eurasia Group, said the latest NATO summit showed that the West and its opponents appeared to be positioning themselves in a "new Cold War posture."

China being labeled as a principle adversary would, he said in emailed comments Monday, increase "pressure for decoupling from China in strategically important sectors for the Europeans...and given the presence of Asian allies as strategic partners to NATO, increasingly feels to Beijing like broader containment that could move the world into a new Cold War posture."

Just how the West can confront such adversaries remains to be seen. Russia, North Korea and Iran are already under substantial international sanctions, and those restrictions on trade and key sectors have arguably pushed them closer together.

Lumping China in with so-called "rogue states" was a significant step for NATO, one security expert noted, but it still did not give any clarity on how Western allies might confront an adversarial axis of power.

"The declaration states that 'The PRC [People's Republic of China] cannot enable the largest war in Europe in recent history without this negatively impacting its interests and reputation', which is a significant step for the Alliance in calling out its hostile intent," said Ed Arnold, a senior research fellow for European Security within the International Security department at the Royal United Services Institute think tank.

"However, it mainly identified and admired the problem, rather than outlining what NATO should do about it," he noted in commentary last week.

Holger Schmieding, chief economist at Berenberg Bank, said the West's economic superiority could help it prevail, while its adversaries are putting severe strain on their own economies and resources — whether through waging war, in the case of Russia, or by supporting conflict elsewhere, as per North Korea and Iran.

"In an increasingly multipolar world, the free and advanced democracies of the Global West are facing ever more challenges," Schmieding said in emailed comments on Monday.

"Russia is waging a high-intensity war against a fellow European country while China is aggressively asserting its power," he noted.

"It is easy to be pessimistic about the outlook for the advanced countries as defenders of freedom, peace and democracy. But that would be wrong. Time is not on the side of the enemies of the Global West. China's share in global GDP [gross domestic product] seems to be peaking, Russia will struggle to wage its costly war for more than a few more years and Iran is turning ever more into what North Korea already is, an economic basket case with very limited resources."

The "Global West" has superior resources, Schmieding said, and, "if it musters the will to use its might, support Ukraine, pay for its defence and play the long game, it can prevail while the troublemakers suffer the consequences of having overstretched their economies."