If you're the most advanced in terms of science, or leading the pack in terms of score, you can expect hostility from the AI. Power alone won't dissuade them: my global empires have been challenged by rump states and single-city powers in recent games. This is why I prefer disabling powers on my own continent (by reducing them to rump states with no resources like iron, horses, saltpeter, and rubber). Other powers may still attack, but fighting off troop landings is much easier than land invasions.
