Conversation so far:
What is the background of Tosca?
In the early 1880s Sardou began a collaboration with actress Sarah Bernhardt, whom he provided with a series of historical melodramas.
Did Sarah Bernhardt play a role in Tosca?
His third Bernhardt play, La Tosca, which premiered in Paris on 24 November 1887, and in which she starred throughout Europe.
Where all did they take La Tosca in Europe?
with more than 3,000 performances in France alone.
How was it received?
La Tosca, which premiered in Paris on 24 November 1887, and in which she starred throughout Europe, was an outstanding success.
What made it so popular?
CANNOTANSWER.
Is there anything else interesting about the background of this opera?
he wrote to his publisher, Giulio Ricordi, begging him to get Sardou's permission for the work to be made into an opera: .

Question: Why did he need Sardou's permission?
Self-contained rewrite: Why did Puccini need Sardou's permission?