‘Quarrel’ is related to ‘War’ in the same way as ‘Error’ is related to ‘_________’.

Blunder

‘Quarrel’ is related to ‘War’ in the same way as ‘Error’ is related to ‘_________’.

The logic followed here is :

Quarrel is a heated argument or disagreement

And

War is a state of armed conflict between countries or different groups within a country

Both mean to fight against something

Similarly

Error is a mistake

and Blunder is a careless mistake

Error is related to blunder