Hybris
Dreamer
A simple example I didn't found : the roman Empire, during the first four centuries. Every one knows they were polytheists under César and the first Princeps (Emperors), but strangely, we oftenly forget that at the fall of the Empire, they were totaly monotheist, the christian religion being the State religion. So : during the first century, the christians were persecuted (depending of the location and the date - it wasn't every time), then quite tolerated, then the Princeps religion (Constantin, ~320), and finally the sole State religion, under Theodose, in 392. The rise of a monotheist religion replacing a monotheist one might an interesting concept. Because, of course it wasn't as linear as it look there, and there were a lot of conflicts (did you asked for pacific relations ?), but there was a coexistence, and at a time, a balance, probably.