As tensions escalated between Europe's great economic powers, most local banks stopped honouring foreign letters of credit.
Since pioneering the improved security of foreign payments in the 1800s, American Express was one of the few businesses to continue facilitating crucial international payments via bank drafts.
This service provided relief to nearly 150,000 travellers and troops stranded on the continent without access to funds.
As war raged on, the company was appointed an official agent of the British government, tasked with delivering relief parcels, letters and money to British prisoners in Bulgaria, Germany, Holland, Norway, Switzerland and Turkey. American Express employees were authorised to access prisoner of war camps and arrange for British and French prisoners to access bank drafts.