The Lost Civil War is fought between a large faction led by Brian Jeremy and a smaller faction led by Johnny Klebitz in the events of Grand Theft Auto IV: The Lost and Damned. The participants are Johnny Klebitz, Jim Fitzgerald, Brian Jeremy, Clay Simons and Terry Thorpe.
The Start of the War
The Lost Civil War started immediately after Billy got arrested in Chinatown, Brian who also came along strongly believed that Johnny ratted Billy out. Meanwhile Brian tries to get his supporters. This begins as a rivarly.
The Middle of the War
Later on, Johnny meets up with Jim, Clay and Terry. Jim says Brian wants a truce after what he said to Johnny, since he already hates Brian, they all decide to take him out. They meet with him at the Port Tudor docks, and unsurprisingly, it doesn't go well. But it looks like Brian persuaded many Lost bikers to join his side. While Brian rushes out of the fight and leaves his army to fight Johnny, Jim, Clay, Terry and three other loyal bikers. After the big shootout, Johnny and Jim chase and finish off the rest of Brian's faction.
Johnny, Jim, Terry and Clay meet up with Ray Boccino who Billy was meeting with before. Now he tells them that the civil war they're having is very bad for his business and advises them to finish this off and get back to work. Ray tells them where Brian is hiding. So Johnny goes to his safehouse (he can call Clay and Terry for backup if the player wants to) and fights off the rest of them.
Once Johnny reaches Brian, he chooses to either kill him or spare him, if you kill him, that's it. But if you spare him, he'll appear as a random character. He leads Johnny to another suprise attack, Brian's supporters get killed and Brian doesn't get a second chance. Whichever choice you make, Johnny's faction emerges victorious.