In 1954, the Soviet Union suggested that it should join NATO to preserve peace in Europe. The NATO countries, fearing that the Soviet Union's motive was to weaken the alliance, ultimately rejected this proposal. The incorporation of West Germany into the organization on 9 May 1955 was described...
We've had 60 odd years of peace in western Europe as a consequence of the EU, by comparison the list of conflicts before then is rather long.......
69 Year of the Four Emperors
193 Year of the Five Emperors
238 Year of the Six Emperors
284-285 Roman civil war
306-324 Civil Wars of the Tetrarchy...