In 1915 Lieutenant-Colonel Christopher Thomson, a fluent French speaker, was sent to Bucharest as British military attaché on Kitchener's initiative to bring Romania into the war.

But when there he quickly formed the view that an unprepared and ill-armed Romania facing a war on three fronts against Austria-Hungary, Turkey and Bulgaria would be a liability not an asset to the allies.

In exchange, it was to receive the following territories: The exact borders stipulated by the treaty were those of prewar Romania (Article I) and those it was allowed to annex from Austria-Hungary, up to a line of demarcation described in Article IV:[5] The line of delimitation will start on the Pruth at a point of the present frontier between Roumania and Russia near Novoselitza and will ascend this river as far as the frontier of Galicia at the confluence of the Pruth and the Ceremos.

[7] The military convention stated that Romania was to attack Austria-Hungary from the south while Russia committed itself to start an offensive on the Austrian front to support the Romanian advance into Transylvania.

Thompson, now head of the British Military Mission, had to alleviate the consequences of Romania's capitulation, and he personally supervised the destruction of the Romanian oil wells to deny them to Germany.

The toll of the campaign was approximately 220,000 dead for Romania, but in the end it gained Transylvania, two-thirds of the Banat, Bukovina, and Bessarabia in the Treaty of Trianon.