If international relations are a seamless web, then the crisis over Russia's actions in Ukraine risks entangling other knotty current issues – from efforts to contain Iran's nuclear ambitions, through the continuing carnage in Syria to wider disarmament ambitions.

For all the echoes of cold war days in the standoff over Crimea, its repercussions could affect some of the toughest problems of today's multipolar world, in which US power is perceived as being in retreat and Barack Obama has been criticised at home and abroad for a reluctance to use force and failure to act decisively.

Given the current tensions, it seems highly likely that wider US-Russian co-operation will become harder. That matters: without agreement between Moscow and Washington, a deal would not have been possible after last year's Syrian chemical weapons crisis, which briefly threatened a dangerous escalation of the war. And Syria's agony is still far from over.

Looking ahead, without Vladimir Putin's goodwill Obama may well find it far harder to manage the complex logistics of the long-awaited withdrawal of US forces from Afghanistan.

On another sensitive front, analysts have warned that Iran may feel emboldened by the confrontation between Russia and the US, because so much depends on their collaboration. "From the Iranian point of view," commented George Friedman of the Stratfor consultancy, "the US urgency to make peace [with Iran], along with Russia's interest in impeding Washington's progress, could temporarily boost Tehran's leverage in talks with Washington."

Israel, which is concerned to maintain its own (undeclared) nuclear monopoly, and which is deeply suspicious of the western rapprochement with Tehran, appears worried. A Jerusalem Post correspondent warns: "Putin may strike back at western responses to his Ukrainian moves – such as trade sanctions and kicking Russia out of the G8 – by actively undermining US and western policy regarding Iran, or working against the current diplomatic process with the Palestinians."

Russia, some US officials reportedly fear, may even move to torpedo a final deal on the Iranian nuclear dossier by striking its own bilateral energy agreement outside the negotiating framework of the P5 + 1 (the five permanent members of the UN security council, plus Germany). But Sadeq Zibakalam, of Tehran University, doubted the row between Russia and the west would benefit Iran because, he said, Moscow's position was weakening.

Asian commentators have suggested that if the US and Europe allow Russia to take over Ukraine unchecked, North Korea and China are also likely to behave more aggressively in future.

The crisis looks like good news for Syria's president, Bashar al-Assad. It will surely lessen the already slim prospects of pressure from Moscow – his most important international supporter – to make any significant concessions to the rebels fighting to overthrow him.

Putin's insistence that Russian forces in Crimea are in fact Ukrainian "volunteers" echoes the crude propaganda of the Syrian war. And hopes that the Geneva II talks would map an exit strategy to end the conflict had, in any case, faded before Ukraine blew up.

It seems a long time since the famous "reset" of US-Russian relations early in Obama's first term. Progress then included the "new start" treaty to reduce nuclear weapons, and Russia's membership of the World Trade Organisation. The White House also hoped for enhanced co-operation with the Kremlin over North Korea, Afghanistan, trade, and military-to-military engagement.

Arms control experts warn now that the outcome of the Ukraine standoff will have an impact on nuclear nonproliferation. International security assurances were central to persuading Kiev to agree to get rid of its nuclear arsenal in 1994, under the terms of that year's Budapest Memorandum.

Moscow, it is worth recalling, pledged then "to respect the independence and sovereignty and the existing borders of Ukraine", and "to refrain from the threat or use of force against the territorial integrity or political independence of Ukraine".

If Washington and London fail to stand by that commitment now, it would clearly discredit the idea of such assurances. However, or whenever, this crisis ends, the ripple effect will be felt far beyond Ukraine's borders.