The British first became involved with Salonika in October 1915 to assist Serbia and Greece. The Allies were forced out of Serbia and retreated. By December 1916 the Allied line was established about 20 miles north of Salonika, with the British holding the East and the French the West. At the Battle of Doiran in May 1917, the British failed to make any significant progress against Bulgarian positions.
With the failure of the larger Allied offensive involving the French and Serbs, the area was effectively inactive until 1918. Then, in September 1918, and as part of a wider Balkans offensive, the British attacked again and assaulted the defences around Lake Doiran. The attack was a failure but it did prevent the Bulgarians moving in units to repair their broken front further East. At the end of September the Bulgarians were conducting a general retreat. On 30 September an armistice was signed between the allies and Bulgaria.
British involvement in the Italian campaign was due to the collapse of the Italian Army at the Battle of Caporetto. In late October 1917 the British were asked to provide assistance. In all, six infantry divisions and a brigade of cavalry together with supporting formations were ordered from France to Italy. With the front stabilised, one division and one corps were ordered back to France in February 1918.
After months of being on the defensive, the Allied forces attacked in late October and fought the Battle of Vittorio Veneto (24 October - 4 November 1918). The battle was a success, throwing the Austrian forces back over a wide area and causing a general withdrawal. By 2 November the Austrian frontier was crossed in several places. On 4 November an armistice came into effect between the Allies and Italy.