We have'th our own will!
Frog is from 600 AD - Middle Ages. During this time there is a war going on with the Mystics. The Mystics are a group of magic users bent on destorying Guardia Kingdom. There is no good side or bad side. It's war and the only side is losing. The Knights do their bests to hold off the Mystics but they have suffered a great loss. It's only when Magus goes missing is the human army able to defeat the Mystics.
Now, Chrono Trigger's Middle Ages are similar to our own Middle Ages. The Middle Ages take place after Antiquity or the Dark Ages as early Middle Age is also called. 12000 BC is called the Dark Ages (Antiquity in the Japanese verson) and then the next timeline is 600 AD the Middle Ages. Now in this timeline a lot is going on, there are knights, plagues and new religions. Our time is the start of Islam with Muhammed this would be similar to Magus's role in the game. A prophet would rise up and teach others. Magus did this and rallied the mystics to war with the knights. Muhammed didn't end up in war. So there are some differences or histories got small parts from each merged into one. But the most commom theme is the knights.