Well,since you're on the hard setting,you will get this(CA have this time foucsed on the conteny)
My solution is this.
Since you begin 1467 to 1600.I dont think it is wise to rasie a big army at the year 1467,then take it off somewhere to conqer,then the Ai come in your captial.
To prevent this,you must first get rid of rebel armies in your border.Get rid of any other armies getting in your border.Bulid a navy,(Will be helpful)
It would
...