<a href="https://en.wikipedia.org/wiki/World_War_I" id="mwqw" rel="mw:WikiLink" title="World War I">World War I</a>: The <a href="https://en.wikipedia.org/wiki/American_entry_into_World_War_I" id="mwrA" rel="mw:WikiLink" title="American entry into World War I">American entry into World War I</a> begins when diplomatic relations with Germany are severed due to its unrestricted submarine warfare.