NATO Secretary General Mark Rutte warned Thursday that members of the alliance could be “Russia’s next target,” calling for a rapid rise in defense spending to prevent a war similar to those seen by past generations.

NATO Secretary General Mark Rutte on Thursday delivered dire warnings about Russian President Vladimir Putin and the growing threat of war that Europe faces from the Kremlin. Why it matters: Rutte warned that Putin won't stop his aggression with Ukraine and could look to attack NATO countries within five years.

NATO Secretary General Mark Rutte warned that Europe must prepare for a war on the scale “our grandparents endured,” as he accused Vladimir Putin of returning to an “empire-building” mindset during a speech in Berlin.