Ukraine crisis likely to increase divisions between US and Russia
Divisions between US and Russia could grow in the fallout from Ukraine
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 carnage in Syria to wider disarmament ambitions.
For all the echoes of cold war days in the stand-off 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 for a 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 nuclear monopoly, and which is 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."
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 Syrian President, Bashar al-Assad. It will surely lessen the already slim prospects of pressure from Moscow - his most important international backer - 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 the Ukraine crisis 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 engagement.
Arms control experts warn now that the outcome of the Ukraine stand-off 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.