Final answer:
Victor Hugo went into exile for 19 years after declaring Napoleon III a traitor to France, due to his forceful seizure of power and his self-declaration as Emperor.
Step-by-step explanation:
The individual who went into exile for 19 years after declaring Napoleon III a traitor to France was Victor Hugo. A revered poet, novelist, and dramatist, Victor Hugo became a vocal critic of Napoleon III, who seized power in a coup d'etat and declared himself Emperor. Due to his opposition and fear for his safety, Hugo left France in 1851 and lived in exile until 1870. During those years, Hugo continued to write and express his political views, further solidifying his reputation as one of France's greatest writers.