WW1 wasn’t “started by preparation”. In fact it was the continuation of about 100 years of war, and the war continued for nearly 100 years afterward. Europe had been at war nearly continuously from Napoleon to 2000 .
The partition of Europe between the two victors of WW2 (USA and USSR) was part of the peace, not a state of war. The cold war wasn't a war inside Europe but between two rival superpowers; the Yugoslavia war wasn't one between EU countries but a civil war result of a change in external conditions.
And Stalin continued to take territory even later, moving into East Germany, Czechoslovakia, etc . Continuing with military pressure over the later years.