There is a confirmation when you declare war on another civs! At least in my games there was always a request of confirmation that went as followed: "You're right! They are scum!" (YES) and "No! We should respect our neighbours" (NO)!
I don't know why it doesn't appear to you! Maybe it's an option that can be disabled, or maybe they declared war on you!
BTW, The "remove your troops from our territory or declare war" may lead the other civ to declare war on you - there is no confirmation for this, obviasly!
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Portugal
Nation of: Magellan's (from Magellan's Expedition);
Vasco da Gama (Discoverer of the Maritime path to India);
and Pedro Álvares Cabral (Discoverer of Brazil in 1500)