We investigate in an economic experiment how people choose sides in disputes. In an eight-player side-taking game, two disputants at a time fight over an indivisible resource and other group members choose sides. The player with more supporters wins the resource, which is worth real money. Conflicts occur spontaneously between any two individuals in the group. Players choose sides by ranking their loyalties to everyone else in the group, and they automatically support the disputant they ranked higher. We manipulate participants’ information about other players’ loyalties and also their ability to communicate with public chat messages. We find that participants spontaneously and quickly formed alliances, and more information about loyalties caused more alliance-building. Without communication, we observe little evidence of bandwagon or egalitarian strategies, but with communication, some groups invented rank rotation schemes to equalize payoffs while choosing the same side to avoid fighting costs.