I want to know the answer to the following question:
By what year had the situation in Europe cool down enough so that Joao VI would have been able to safely return to Lisbon?
All the background I'm provided with is that "Portuguese and their allied British troops fought against the French Invasion of Portugal and by 1815 the situation in Europe had cooled down sufficiently that João VI would have been able to return safely to Lisbon.". Is that enough to answer the question?