What year European nations joined World War 1

Few nations in Europe were able to stay neutral in the First World War. Though the main great powers started the conflict in 1914, the need to open new fronts to break the stalemate of trench warfare would cause prior neutral states to join the war up until 1917.
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Links to learn more!! (You really should!):
War Declarations - https://familytreemagazine.com/history/ww1-war-declarations-timeline/
Interesting Facts - https://www.iwm.org.uk/history/5-things-you-need-to-know-about-the-first-world-war
Trench War Game! - https://www.warmuseum.ca/overthetop/game/