Not necessarily. Depending on how long your secret world has existed, there is a thousand years worth of time for different factions/clans/races to act. It would be super unrealistic if those within it only had the idea to take over the world at the back end of those thousand years.

Think of the societies we have now in our world. It doesn't exactly take long for them to go to war over land or plunder. What makes *this* faction, which is by necessity so MUCH more powerful than everyone else, different in that regard? What motivation do they have to STAY secret?