World War I: The <a href="https://en.wikipedia.org/wiki/Kingdom_of_Romania" id="mw1Q" rel="mw:WikiLink" title="Kingdom of Romania">Kingdom of Romania</a> declares war on <a href="https://en.wikipedia.org/wiki/Austria-Hungary" id="mw1g" rel="mw:WikiLink" title="Austria-Hungary">Austria-Hungary</a>, entering the war as one of the <a href="https://en.wikipedia.org/wiki/Allies_of_World_War_I" id="mw1w" rel="mw:WikiLink" title="Allies of World War I">Allied nations</a>.