As Old Kaspar says it, it was a war between the English and the French. The English defeated the french in the Battle of Blenheim.
 
During the war, a vast countryside was destroyed with swords and fire. Many people including childing mothers were killed. Many houses were burnt. Many were forced to flee from there without any place to rest their heads. Kaspar’s own family was in the list of victims. 
 
Again, in the war, many soldiers were killed. When the ‘field was won’, many thousand bodies lay rotting in the sun.
 
It was a shocking sight. But stereotype people like Kaspar thinks things like these happen in every ‘great victory’. And here lies the irony of the poem. The poet expresses the pity of war through his poem.