PLOT RUNDOWN:
To get things straight, for the people who lost track during the film, in the beginning of the film, Crawford (Jason Statham) is an FBI agent who's partner is killed by a member of the Yakuza named Rogue (who was believed to be a rumor in the beginning of the film). Rogue comes to Crawford's partner's house and kills him, his wife, and daughter (as well as burns down the house). Crawford, his wife, and his daughter arrive at their house, and see the house burned down. Jason Statham (looking for revenge) finds a bullet that Rogue apparently uses (he found the same bullet in the opening scene of the film) and concludes that Rogue is the killer. Three years pass, and Crawford's obsession for Rogue has cost him his marriage. Him and his FBI team search for Rogue throughout the film.
As the movie progresses, we learn that Rogue (Jet Li) is apparently an assassin working for the Yakuza, who ends up betraying them by joining the Triads, then is secretly betraying (while still appearing loyal to) the Triads by actually working with the Yakuza the whole time. We then see that Rogue is actually setting up both sides, and starting a war (hence, the title) between the Triads and Yakuza by double crossing both of them, and appearing loyal to the other force. As Crawford (Statham) and his FBI team track down Rogue, they find out that various plastic surgeons turn up dead, and also track down one in Tiaquna, Mexico. They learn that Rogue takes on many faces via plastic surgery, in order to be the perfect assassin.
One night, Rogue (Jet Li) and a few Yakuza assassins go to the Triads's headquarters to kill them and their leader. As he proceeds to kill them all, until we then find out that Rogue is not a tough as nails assassin/who he seemed to be throughout the entire film, by saving the wife and daughter (huge important to the finale of the film) of the leader of the Triads [John Lone (aka Ricky Tan

. I was cracking this joke to my friends throughout the whole movie. Even when John Lone died, I said "Damn, he ain't gonna be in
War 2!")] As Rogue double crosses and kills the other Yakuza assassins, who want to kill the Triad leader's wife and daughter, there appears to be a member of the FBI taking pictures of the entire event. Crawford and his FBI team go to the Yakuza headquarters and show the evidence of Rogue's double cross to the Yakuza leader.
As Rogue goes to the Yakuza headquarters to tell that he completed his task by killing the Triad leader, the Yakuza leader makes it apparent that he knows of the double cross. Rogue and the Yakuza leader have a duel with swords. As Rogue is taking the upper hand, he reveals the details of the murder of Crawford's partner. He reveals he actually is Crawford's partner

wow

. Flashbacks of the beginning is shown, and show that the partner actually ended up killing the original Rogue (who was sent to kill him, his wife, and his daughter). It is revealed that he changed his face and voice, and took on the mantle of Rogue, in order to get in deep enough to seek revenge on the leader of the Yakuza (who ordered the attack from the start). As Rogue is about to kill the Yakuza leader, he mutters "You should have left the wife and child" (which comes full circle to the reason why Rogue didn't kill the Triad leader's wife and daughter). The Yakuza leader then reveals that he ordered the attack based on a tip from Crawford (who was revealed to be working for the Yakuza since the very beginning!

). Rogue then kills the Yakuza leader.
Ultimately, Crawford and Rogue have a final confrontation in an warehouse, where they fight. As they fight, Rogue reveals who he really is. A very shocked/ashamed/sad Crawford says that he double crossed Rogue, but never meant for the Yakuza to kill him. Only to "rough him up." This ends up showing that Crawford's search for Rogue, throughout the film, was not only vengeful, but redemptive. As they continue fighting, Rogue says that he is now the assassin Rogue, and no longer the partner/friend that Crawford once knew. As one of Crawford's snipers positions himself to kill Rogue once he is in the open, Crawford yells "no!" and takes the bullet for his old partner

confused

. Then, after basically no proper resolution, we see Rogue drive off in daylight in his car. The End.