Ukraine had declared a state of emergency due to increased Russian aggression - and early on Thursday morning, Russia launched an invasion.

- This is a typical pre-combat phase where aircraft knock out air forces, air defenses and ammunition depots.

Ukraine has a rather weak air defense and air force, so this phase can take a couple of days, says Magnus Christiansson, senior lecturer in military science at the Swedish National Defense College.

"Relatively easy for Russia"

Katarina Engberg, security policy analyst at the Swedish Institute for European Policy Studies, Sieps, believes that Putin will now gradually present his demands to the government in Kiev to demilitarize Ukraine, say no to NATO and return the weapons it has received from Western countries. 

- Ukraine's air defense is quite weak so this is a first phase of a relatively light operation for Russia.

If Ukraine says no to the ultimatum, Russia will continue the invasion with ground troops, says Katarina Engberg.

Uses military superiority

Oscar Jonsson, PhD in Russian warfare at the Swedish National Defense College, recognizes parts of Russia's approach from how it acted in eastern Ukraine in 2014. 

- But what is happening now is not a surprise operation, rather they have built up military equipment over a period of ten months and use military superiority, says Oscar Jonsson in Morgonstudion.

Prepared for long operation

- To put this in perspective, Russia used at most around five battalion battle groups in eastern Ukraine in 2014. Now there are about 115 that stand around the whole of Ukraine and can be used.

What has been going on in eastern Ukraine for eight years has been limited, while this looks to be potentially the biggest war since the Balkan War or World War II, he says. 

According to Jonsson, the fact that Russia has been prepared with field hospitals, blood banks and engineering regiments has indicated that Russia wanted to "take and retain terrain for a long time".

- Russia has absolutely enough military capability to fight the Ukrainian army and take eastern Ukraine.

But what happens in war also depends a lot on chance, will and determination, which is difficult to judge from the outside.