I was a bit slow too, just having fun fight's, getting renown, becoming marshall, reconquering lost castles and a town (Ishkoman), later being awarded with it. Then I saw my husband (Hrothgar the Fat - he was the only one who would marry me
), an enemy lord, raiding one of our kingdom's villages so i went there to check the dialogue options with him. I didn't pay much attention to it though, clicked on something and poof, we both seceded from our kingdoms and formed a new one
Of course there was a reprisal raid from my former liege but to my surprise i withered it easily with masses of bladesmen and dervishes on the battlements, while i was hiding behind a wall as to not invite a misfortune
After that i've garrisoned the city with 200 dervishes and 100 bladesmen and other troops to the total of 500, which made my enemies avoid it like plague. Later i've replaced the bladesmen with cheaper pendor swordsmen, cca 150 now. The present day is 729 and i've only just begun