A distinction between diplomacy as independent variable, impacting upon other developments, and diplomacy as dependent variable, adapting to other causes, is employed to underpin focused case analysis of negotiation between states. To dramatize diplomacy as dependent variable, it is hypothesized that allies with convergent interests would find negotiations between themselves more difficult when domestic constraints such as political ideology and pressure group activity intrude. To highlight diplomacy as independent variable, it is hypothesized that adversaries with divergent interests employ diplomatic statecraft to reduce the chances of war in periods of confrontation. Using a relatively small case sample, this study confirms these hypotheses, but reveals similarities as well as differences between the case categories. It is argued that the focused case approach is a fruitful way to yield much-needed generalizations about diplomatic statecraft.