A strong external military force, along with the devastation of European countries with global ambitions in WWII (UK, French, Germany, and co), means there were neither resources nor reason for war in Europe for most of the 20th century. Heck, for most of that time Germany was still split in two.

USSRs occupation of the other half also kept "peace" there (and in conflict between the two sides would have escalated to a full global war, which was in nobody's interest).

Yugoslavia for example was only a state because the different nations were kept under the same rule. When that rule was gone, 60 years of "living together" didn't do anything to prevent ethnic tensions.

How things shape in 10 or 20 years is anybody's guess.

That's an intense exaggeration. The military deployment in Europe during WW2 was drastically beyond anything that existed during the Cold War. The US had 16 million people that served in the armed forces during WW2. Roughly more Americans died fighting that war, than were stationed in Europe during the Cold War at a given time (average was about 330k from 1950 to 1990).

The military deployments in Asia from 1930-1945 were larger than anything Europe saw from 1945-1991, by several fold. China alone had roughly four million soldiers active at the end of WW2. Japan had millions of soldiers and civilians stationed in China at the time they surrendered.

About ten million military personnel died in WW1. That one point alone puts to shame the scale of the Cold War. The US, Russia, British Empire, France, Italy mobilized nearly 40 million military forces during WW1. The Cold War was tiny by comparison. France by itself had 1.3 million soldiers killed. Russia had five million wounded soldiers. Including the two sides, over 60 million military personnel were involved in WW1.