No, not the people. What was at home was the
symbol. It was about why they were fighting - what they were fighting
for.
putting the sentence the other way round:
the symbol of what the nation's military might was safeguarding
was
the menaced
sanctuary of
the domestic firesidemenaced - under threat
sanctuary - safety
domestic = in the home
fireside = family gathered round the fire, cosy and safe and warm.

What was the army safeguarding? What was their motivation?
To win territory in France?
To conquer Spain?
To stop the colonies from rebelling?
To free Jerusalem?
No.
What was the symbol of what they were fighting for?
What did they fear would happen if they
lost?

The coalition won, and Napoleon never successfully invaded Britain. But what if the British had
not won their wars?
They made jokes about the French invasion, and in the end the only attempt failed. But he had been unstoppable across Europe.

There is a difference between fighting a war in France or America, and fighting to stop a perceived threat of invasion, where an invading army is going to attack your wife and children in their home if you don't stop them abroad.