The Kingdom of Portugal had been allied with England since 1373, and thus the Republic of Portugal was an ally of the United Kingdom. However, Portugal remained neutral from the start of World War I in 1914 until early 1916. However, in that year and a half there were many hostile engagements between Germany and Portugal. Portugal wanted to meet British requests for aid and protect its colonies in Africa, causing clashes with German troops in the south of Portuguese Angola, which bordered German South West Africa, in 1914 and 1915.

The First Portuguese Republic spans a complex 16-year period in the history of Portugal, between the end of the period of constitutional monarchy marked by the 5 October 1910 revolution and the 28 May 1926 coup d'état. The latter movement instituted a military dictatorship known as Ditadura Nacional that would be followed by the corporatist Estado Novo regime of António de Oliveira Salazar.