Subjugatin' ain't easy. You can't just show up and expect everyone to give you their stuff and obey what you say. People ask inconvenient questions like, "who the heck are you?" and "from whence do you derive your authority?" If your reply, "The Lady of the Lake, her arm clad in the purest shimmering samite, held aloft Excalibur from the bosom of the water signifying by divine providence that I, Arthur, was to carry Excalibur. That is why I am your king" doesn't work, it is time to resort to violence.
History is full of brutal subjugation techniques. The tools of psychological terror range from heinous torture to nauseating violence and dismembered corpses. What really seems to do the trick, however, are public spaces festooned with human remains. Nothing enables tyrannical oppression like the public display of dead bodies. When peasants see a dead guy with his eyes gouged out hanging from the castle walls, they're generally too busy pissing themselves to think about rebellion.
Nothing Says "Obey Me" Like a Head on a Spike
King Edward Longshanks Had "Traitors" Hanged, Drawn, and Quartered
The Romans Crucified Just About Anyone Who Pissed Them Off
Vlad the Impaler Really Earned His Nickname