Declare War Against Your Enemies

Brush up on Sun Tzu's The Art of War and grab your helmet. It's time to declare war on your enemies.
We have updated the Declare War feature so that you go to war against rivals instead of your friends/frienemies. We have included 10 new awesome rewards and a new achievement that you can only get from winning wars.
Here's how you go to war.
1. Make sure you have assigned your top 6 mafia members. You can do that by clicking the "My Mafia" tab and picking 6 friends to fill up those top slots. A friend's class (Fearless, Maniac, or Mogul) determines which position (ie Bodyguard, Bagman, Wheelman) you can promote them to.
2. Go to the Declare War page and pick an enemy to attack. Your war lasts 16 hours, and you can only declare one war each time.
3. Recruit your mafia to go to battle with you. The more friends that help you bring down your enemy, the better chance you have to win. Friends get "Helper rewards" if you win your war. Friends can help fight in as many wars as they want, but can only receive "Helper rewards" for the first 5 wars they contribute to.
4. Below are all the items you can win from Declare War. Earn all 16 Declare War rewards to gain the Warlord Achievement. Play Mafia Wars and pummel your opponents now!

Item	Attack	Defense	Type	Rarity
Cañonazo	42	22	Weapon	Common
Big Bad Wolf	42	25	Weapon	Common
Tanto	43	28	Weapon	Common
String of Firecrackers	33	46	Weapon	Common
Raed Armored Sedan	30	47	Vehicle	Common
Deadly Impression	28	47	Vehicle	Common
Cataclysmic*	53	26	Vehicle	Uncommon
Savanna Baboon*	25	54	Animal	Uncommon
Snapping Turtle*	56	25	Animal	Uncommon
Duster*	27	56	Armor	Uncommon
Spiked Baton*	58	28	Weapon	Uncommon
Armored Biker Boots*	27	59	Armor	Uncommon
Contender*	33	63	Vehicle	Rare
Galapagos Hawk*	64	32	Animal	Rare
Growler*	33	65	Vehicle	Rare
Hack N Slash*	65	35	Weapon	Rare

http://blog.mafiawars.com/2010/09/declare-war-against-your-enemies.html