King of the Hill is series of battles between leagues to occupy and hold different locations for a specified period of time. It is the only way to receive the kingdom tax (regional and national) and other prize.
From the beginner guide: (http://forum.koramgame.com/forum.php?mod=viewthread&tid=3771)

• King of the Hill lasts for 30 minutes for both regional and national wars.
• Regional War: Starts every Saturday at 10:00-10:30 (PST)
• National War: Starts every Sunday at 19:00-19:30 (PST)
• The first attack may be sent out at exactly 10:00 and 19:00 respectively
• NPCs will defend the city first. When the NPCs are destroyed, players will defend the city.
• Players from opposing leagues will attack each other.  (Does not matter if the league is a "sister league")
• Players from the same league will help defend each other.
• King of the Hill is where players can receive a tax license.
• Capitals are defended with units that have the high defence.  Units that have a lower defence rating than your main defence unit already defending the capital will be sent back to your city.

Other thing they forgot :

– The time provided here is not always true, they sometime change the time to accommodate players who cannot play in those hours.

– Troop deployed to a King of the Hill target (KoTH) will take the same amount of to reach the city, you troop speed, heroes ability and upgrade have no influence on the time. However you state location have an influence on how much time it will take to arrive at destination. It for minute if you are in the same region (north, east, west, south) than the capital and 8 if you are outside.  here how north, east, west, south is separated :

– Regional KOTH targets can hold up to 2,000 player defending units. National KOTH targets can hold up to 5,000 Player defending units.
– They are 6 prizes per city in the regional and 9 for the national war.
note that only the following player that achieves the following goal will receives a revenue license (tax) (among other prize).

Master of Marching: Player who occupies the target city for the longest time.
Lord of Slayer: Player who have the most Kill
Lord of War: Given randomly to any player who occupied the KOTH city during the event.

On revenue license (tax permit) : Regional war give the tax permission for your region and national war give it to the whole server. When you have it you need to chose a league to tax.
You get a lot of resources when you use it , it always depends on which league your tax but it always a decent amount my lowest was around 150k of each resources and highest 500K-600k.

Tips and tactical note:

I noticed player knock out the troop then leave to prevent lost, so that mean you can always try to send from you sub and you might be able to grab a city (this happen specially in the regional)
Just by occupying the city you can get the lord of war so it might worth it.
I haven’t really try any fancy tactic, most of the time there not much players that are doing it any way since for some of us its during office hour or in the middle of the night.
Most of the time if you’re in the top league you’ll end up hitting your own sister league or supporting your league member if you arrive late, so try not to be late.

However if you have a huge force it can help you get kill and become Lord of slayer, then withdraw your troop to prevent lost.

Hope it help and check those guide with image and stuff for more info on King of the hill.

Original post on KOTH on koram main site

Beginner guide to KOTH

Gehrshi On King of the Hill