According to thoreau to what does a person owe the strongest allegiance

Henry David Thoreau motivated people to be truthful and loyal, his main objective in writing was the unfair government.

Making a big emphasis on slavery and war, many of his arguments talk about changing the government by doing what we consider right.

A very important moment in his life, which made him write the book civil disobedience, was the legal conflict he had due to his refusal to pay taxes to a government who according to his opinion didn't deserve it.  

Having a heavy political an civil opinion he always showed that the biggest allegiance of man should be to the truth and to do the right thing as a society.

The answer is "radioactive".

Explanation:

"Ten o'clock. The sun came out from behind the rain. The house stood alone in a city of rubble and  ashes. This was the one house left standing. At night the ruined city gave off a radioactive glow  which could be seen for miles. "