Britain's conduct for World War I was based upon international coalitions, paritcularly her partnership with France. This drew Britain into war, since French defeat would fatally upset the European balance of power. The allies' relationship was, however, often stormy, but Britain's primary goal was its preservation. Ironically, it was an operation which had little effect on the outcome of the war that posed the greatest threat - the "Salonika campaign", showing the allies' conduct at its worst. Here the Anglo-French sources achived little, but the diversion seriously weakened the armies on the Western Front. Drawing on previously unopened archive material, this work shows the campaign as central to the war-time alliance, and the issues revealed transcend the importance of the Balkan campaign itself.