Arguments in the foothills of war are always the same. Those for war shout loudest and beat their chests, eager for tanks to rumble and jets to roar. Those against are dismissed as wimps, appeasers and defeatists. When the trumpets sound and the drums beat, reason runs for cover. The visit to Taiwan of the US congressional speaker, Nancy Pelosi, has been so blatantly provocative it seems little more than a midterm election stunt. She declares it “essential that America and her allies make clear that we never give in to autocrats”. China’s gross overreaction is a classic example of precipitate escalation. Yet when Joe Biden asserted that the US would defend Taiwan militarily, the president’s office instantly backtracked, reasserting a policy of “strategic ambiguity”. It remains the case that no one quite believes the US will go to war over Taiwan – so far. A similar ambiguity infuses the west’s attitude towards Russia over Ukraine. The US and Britain reiterate that Russia “must fail and be seen to fail”. But can Russia really be relied on to tolerate ever greater destruction of its armaments without escalation? The west seems set on holding Ukraine to a drawn game, hoping to postpone some horrific penalty shootout. All Russia can do is perpetrate ever more atrocities to keep its team in play. Suppose it escalates something else? These are the same uncertainties that overwhelmed European diplomacy in 1914. Rulers dithered while generals strutted and rattled sabres. Flags flew and newspapers filled with tallies of weaponry. Negotiations slithered into ultimatums. As the frontline pleaded for help, woe betide anyone who preached compromise. During the two east-west nuclear crises of the cold war, in 1962 over Cuba and 1983 over a false missile alarm, disaster was averted by informal lines of communication between Washington and Moscow. They worked. Those lines reportedly do not exist today. The eastern bloc is led by two autocrats, internally secure but paranoid about their borders. The west is blighted by weakened and failing leaders, striving to boost their ratings by promoting conflicts abroad. What is new is the conversion of the old western imperialism into a new order of western “interests and values”, ready to be prayed in aid of any intervention. Such an order has become arbitrary and knows no boundaries. Despite Pelosi’s claim, the west “gives in” at its own convenience, intervening or failing to do so. Hence wayward policies towards Iran, Syria, Libya, Rwanda, Myanmar, Yemen, Saudi Arabia and others. Britain abandoned Hong Kong to China and donated Afghanistan to the Taliban, the futility of the latter intervention shown last week in the drone killing of al-Qaida’s leader in Kabul. Never in my lifetime has the Ministry of Defence had to defend my country against a remotely plausible overseas threat, least of all from Russia or China. Instead, in the cause of “interests and values” it has killed untold thousands of foreigners in my name and to virtually no gain. Now, with the looming threat of a serious east-west confrontation, the least we should expect of Britain’s probable next prime minister, Liz Truss, is that she drops her cliches and articulates clearly what she sees as Britain’s objectives, if any, in Ukraine and Taiwan. Neither country is a formal ally of Britain or critical to its defence. Horror at Russian aggression justified military aid to Kyiv, but that was a humanitarian rather than strategic response. Probably the greatest aid we can be to Ukraine is to assist in the eventual return of its exiled labour force and help in rebuilding its shattered cities. Taiwan likewise merits sympathy in its historic struggle with China, but its status poses no military threat to Britain. Its population has long been content with an ambiguous relationship with China as it knows it is at its long-term mercy. Boris Johnson’s dispatch of the aircraft carrier Queen Elizabeth to the South China Sea last year was a senseless act of vanity. Russia and China are both experiencing border disputes of the sort that occur in most corners of the world. Outsiders rarely assist their resolution. The days when western powers could ordain the spheres of interest of states such as China and Russia are rightly over, as was acknowledged during the cold war. Since that conflict ended, the west’s global interventions have become parodies of imperial outreach, notably across the Muslim world. With few exceptions, neither China nor Russia has shown a comparable desire to possess the world. They have merely desired, however callously, to repossess ancestral neighbours. The fates of Ukraine and Taiwan merit every diplomatic support but they cannot be allowed to lurch downhill towards global war or nuclear catastrophe. This may reduce the effect – always overstated – of nuclear deterrence, and make them vulnerable to blackmail. But it is one thing to declare yourself “rather dead than red”, quite another to inflict that decision on others. It may be that one day a global war, like global heating, delivers the world a catastrophe it may have to confront. For the time being liberal democracy surely owes it to humanity to avert rather than provoke that risk. Both sides are now flirting with disaster. The west should be ready to back off – and not call it defeat. Simon Jenkins is a Guardian columnist