Putin had a range of ways to attack Ukraine. He went with the worst-case scenario for the West.

• It is now clear that Russia pursued the most aggressive path to war, as predicted by the US.
• Ukraine was on Thursday attacked from several directions, with troops headed for its capital, Kyiv.

In the build-up to Russia's assault on Ukraine, analysts and leaders envisioned numerous ways the conflict might play out, from a limited incursion to an all-out invasion.

As bombs started to fall and troops moved in to Ukraine on Thursday morning, it was clear that Russia had picked the latter.

"I think [Putin's] gonna go full-bore, get to Kyiv, try and capture [Volodymyr] Zelensky," former NATO Allied Commander Admiral James Stavridis told NBC News, describing a so-called decapitation strategy aimed at Ukraine's president.

Intelligence officials from a Western government, who declined to be further identified, gave a similar assessment at a media briefing Thursday attended by Insider.

Putin used precision missile strikes and airstrikes, followed shortly later by ground maneuvers, the officials said. They said attacks came from the east, south, and north, a description consistent with reports on the ground and Insider's map of the invasion.

All three lines of attack — as per this analysis in The Conversation — had previously been floated as individual possibilities for an invasion.

Defense analysts warned that Russia's multipronged attack was full-scale but still in an early phase, with a lot more forces to push into Ukraine to seize key areas or capture its leadership. Putin's overall endgame remains an area of pressing debate.

Putin's earlier announcement of a more limited intervention in Ukraine's eastern separatists regions in the Donbas suggested that would be the likeliest avenue.

Russia instead chose all of them at once.

The unnamed officials speaking to Insider said that Russia's intent appeared obviously to be to take over and hold large swathes of Ukraine, despite Putin's vow not to occupy Ukraine.

Announcing his invasion, Putin threatened Western leaders with catastrophic consequences should they intervene to help Ukraine, a euphemism widely understood to refer to Russia's substantial nuclear arsenal.

It's a ferocious start that, as The New York Times reported on Sunday, was the most likely outcome in the minds of most military analysts, foreshadowed by the enormous military build-up of over 150,000 troops around Ukraine's borders.

But until around two days ago, it still looked like a softer more limited approach — or even a full retreat — remained on the table.

Out of all actors in this crisis, President Zelensky held out longest for a possible diplomatic solution. On Monday, even after Putin had sent troops to Ukraine's east, he said he didn't believe there would be a full invasion.

Observing the move into the Donbas, Thomas Warren of the Atlantic Council think tank argued that Putin had left the door open for diplomacy. Warren is a former deputy assistant secretary for counterterrorism policy at the US Department of Homeland Security.

Putin, he argued, was using a hybrid warfare approach with the goal of trying "to get real concessions from Ukraine and the West without a real invasion."

But those possibilities blinked out of existence Thursday, with only difficult choices left for Ukraine and its supporters.

Ukraine has pledged to resist, with civilians cleared to take up arms and queues of people seen in Kyiv volunteering to fight. Zelensky activated Ukraine's army reserve in advance of the conflict, and has taken delivery of advanced weapon systems from NATO to even its odds against the massive Russian military.

This kind of resistance will make it more difficult to take Kyiv, but the intelligence officials said Russia's advantages in arms, tactics, and experience — as well as its historical indifference to collateral damage — would be hard to overcome, especially on some many fronts at once.

It left a difficult problem for Western leaders, whose array of sanctions clearly failed to deter Russian escalation.

On Thursday Ukraine requested harsher countermeasures, including a no-fly zone over Ukraine and casting Russia out of the international SWIFT payments system, both far more extreme than anything the West had been willing to do.

It left a choice of totally rethinking the price the West is willing to bear, or leave their ally to its fate.