Ireland was in 1939 nominally a Dominion of the British Empire and a member of the Commonwealth. The nation had gained "de facto" independence from Britain after the Irish War of Independence, and the Anglo-Irish Treaty of 1921 declared Ireland to be a 'sovereign, independent, democratic state'. A new constitution was adopted by a plebiscite in 1937. The Statute of Westminster 1931 meant that unlike in World War I, Britain's entry into the war no longer automatically included its dominions. Relations between Ireland and Britain had been strained for many years; until 1938, for example, the two states had engaged in the Anglo-Irish Trade War.