Has World War Three already started?
Deborah Haynes, security and defence editor
Some security experts believe it has, others say it is only a matter of time until Russia's invasion of Ukraine ignites the spark that triggers an existential, global conflict.
President Putin on Saturday described a decision by the West to impose unprecedented sanctions against his regime as "akin to declaring war".
He is right. The two sides are locked in an economic and political war.
The key question is whether the two sides have the restraint and/or desire to keep this wider conflict beneath the threshold of a full-blown military one.
It is a delicately balanced equation and underlines the fragility and the greyness of the line between what is conventionally viewed as peace and war.
In terms of potential flashpoints that tip the world into armed confrontation, there are many.
Individual allies, including the UK, the United States and even – since Russia's invasion began – previously more pacifist Germany, are attempting to track a middle line between direct intervention and doing nothing.
This involves sending in weapons and ammunition to bolster Ukraine's ability to defend itself.
The end result is not as effective as NATO directly protecting Ukraine's airspace but it is clearly helping Ukraine do what amounts to the same thing. The hope is that Russia will appreciate the distinction.
What if Moscow decides to view the downing of one of its aircraft by a missile gifted to the Ukrainians by America as akin to the US shooting it down directly?
Then look at what a defeat for Ukraine would do. It would have a profound impact on the balance of power in Europe and it could ultimately fuel the appetite of other authoritarian regimes – principally China – to use military force to impose their will over other nations.
Another factor that could make Russia's invasion of Ukraine explode into a wider war is by accident.
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