You will be given a trivia clue, and the category it belongs to. You should answer with the best answer that belongs in the category and is described by the clue. For simplicity, answers should be in all lower cased letters.
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Question: Category: BRITISH HISTORY 
Clue: Dying in 2009 at age 113, British WWI vet Henry Allingham was the last original surviving member of this group, formed 1918

Answer: the royal air force


Question: Category: HISTORIC LASTS 
Clue: In the "thanks a lot, fellas" department, Mongolia was the last country to join this group--August 9, 1945

Answer: the allies


Question: Category: HISTORICAL TERMS 
Clue: Historians refer to "the long 19th century", the 125-year span between these 2 events

Answer:
the french revolution and world war i