World War I broke out on 28 July 1914, pitting an alliance spearheaded by Germany and Austria-Hungary against the forces of the United Kingdom (UK), France, Russia, and their allies. Due to paradigm shifts in military technology, the war quickly turned continental Europe into a charnel house. Nations soon found themselves requiring more manpower than ever before to maintain their war efforts.
In the 1960s, Northern Ireland began a period of ethno-political conflict called the Troubles. Through a series of social and political injustices, Northern Ireland had become a religiously divided society between historically mainland Protestants and Irish Catholics. Furthermore, the Irish people had become a fragmented body over a range of issues, identities, circumstances and loyalties. The conflict between Protestants and Catholics spilled over into violence, marked by riots and targeted killings between the groups beginning in 1968.