Superordinate Goals
Superordinate goals are goals that get people from opposing sides to come together and work toward a common end result. For example, if you have two groups of people that seriously dislike each other you might set up a situation in which they simply have to work together in order to be successful (e.g., maybe the two groups get lost in the jungle together and the only way they survive is to work together - hey, it could happen :). This breaks down barriers, encourages people to see eachother as just people and not as part of "that other group that we dislike", and can help overcome differences between the groups.