Old Kaspar is a common man in Southey’s poem and he represents the common romantic view regarding war. He glorifies the Battle of Blenheim even though he himself was a sufferer when the war broke out.
 
He glorifies the battle by calling it a ‘great victory’ and ‘famous victory’ repeatedly even though he did not know the reason and had no clue regarding what good it brought to the people of the place.

‘Why that I cannot tell,’ said he
‘But ’twas a famous victory.’

Again, when his grandchildren Peterkin and Wilhelmine raised questions about the validity of wars, the old man was firm in his stand that it was a famous victory and the destruction of lives and property is very normal and can be accepted to achieve such great victories. 

But things like that, you know, must be
At every famous victory.

Kaspar also praised the leaders of the battle on the English side.

Great praise the Duke of Marlbro’ won,
And our good Prince Eugene.

Finally, Kaspar’s glorification of the battle was not entirely his fault, but he was a member of the common mass in whom the false propaganda of war was indoctrinated.