To get more land you have to raid with Robin.
The raids seem like they are a waste of time but they will help you in
the long run. Read how much the land is for and you will get more
money for raiding that place.
Prince John will end up taking about 95% of the land with just you
left to kill he is very strong, but there is a way to beat him. You do
raids and pay off the $10,000 ransom for King Richard and you will
only gain 100 knights, but it will help you. Once again read the land
and how much it is worth and this time it will have like difficulty
with is more money, but it is hard. The most money is Cornwell, his
home land and you don't get much time to kill the knights and footmen.
I recommended not to try it, it is a waste of time and will just get
you mad. Take the land that says "Perilous" it is the most
and will give you about $6,000-$9,000 gold and you can build armies
with it. You build massive armies and take land from The Prince and
just keep repeating the raids to get more money and you will
eventually start to take his land and beat him. Get about 300-450 men
in each fortress ( when you take over his land he has all fortress').
He will not attack you because of your massive and powerful armies.
That all I know because this game requires skill and strategy.