I'm sitting with my father watching the television as Russian tanks roll into Ukraine. He was 11 in 1939 when Chamberlain announced war. He tells me how his mother burst into tears at the news. She'd lost three brothers in World War 1.

How are you representing Europe's first land war in nearly 80 years to your pupils? Front and centre? Passing comments? Opportunity for Q&A? Revised curriculum? Nothing unless they ask?

Whatever your approach, try 'jus ad bellum' as a thinking framework.

The principle sets out five conditions for going to war. Here they are with relevant thinking prompts:

1. Proper authority and public declaration
Is Russia a state? Has Russia declared war?

2.  Just cause
Is Russia's purpose to seek/maintain peace rather than pursue narrow national interests?

3. Probability of success
Is there a good chance that Russia's aims (whatever they are) can be met?

4. Proportionality
Does the level of aggression, violence, destruction and the kind of targeting match the purpose?

5. Last resort
Has every other option, every other alternative course of action, failed?

In summary, go to war as lightly as you can, only to seek an achievable peace. Is that what Russia has done?

Derived from the 1945 United Nations Charter, jus ad bellum provides a rational thinking framework and a benchmark from which to judge. It can provide clarity in the midst of chaos.

However, interpretation of jus ad bellum is varied and adherence to it far from guaranteed. It is said that the first casualty of war is truth. The second need not be thought.

Thinking Focus: War