I agree with you that alliances are key for leaders. As I said in my last blog post, which coincidentally was also on relationship building, "Relationship building is one of the most important leadership activity you can engage on. Your influence goes only as far as the quality of your relationships." (http://logosnoesis.com/Carnegie-relationship-building)

In my work with organizations the weakest link many times is alliances between departments, with peers that many times you need to interact with. For some reason, it seems easier for leaders to think on developing relationships with their direct reports and their boss. Yet, they tend to forget that many times their success at work depends on the cooperation of their peers.

Thanks for a great post!