In Europe specifically, it would not be too great of a stretch to say that the main reason there was no further significant war after 1945 was the re-division of Germany.
There was no nation of Germany until 1870; only agglomerations of mini-states, duchies, principalities, etc. When Germany emerged as a unified nation during the time of Bismarck, it sprang full-blown as the strongest power on the Continent. The balance of power which had maintained general peace since the Napoleonic Wars was disrupted.
Until 1990, Germany was a united country for only 75 years of history (1870-1945), and during that time Germany started the two biggest wars ever.
The united Germany is a historical aberration. It is the divided Germany that is the historical norm. The reunification of Germany occurred in 1990. Stay tuned.