Conversation so far:
What were Giuseppe's political beliefs?
"myths intensifying and exaggerating [such] sentiment began circulating" during the nineteenth century.
What were the myths about?
An example is the claim that when the "Va, pensiero" chorus in Nabucco was first sung in Milan.
What effect did he have on politics?
The growth of the "identification of Verdi's music with Italian nationalist politics" perhaps began in the 1840s.

Question: What did that lead to?
Self-contained rewrite: What did the growth of the identification of Verdi's music with Italian nationalist politics in the 1840s lead to?