Each group has its own territory. The territory is very important to the yakuza. When they do business, they cannot break into each other group's territory. If one group tries to break into another's territory it must be protected, usually through violence. In Japan, the general public cannot have a weapon without a permit, but the yakuza do not respect the law.
Many citizens become victims of the yakuza's battles.
When they are fighting, each group tries to kill the boss of the other group, because a group without a boss is weak and has no power to fight. For all members, the boss is God. Without him, they cann ot do anything. Whoever wins the battle takes over the group that lost and their territory. From these battles, one group named Yamada gumi became the biggest yakuza group in Japan.