(yes, I am considering the Caucasus and Asia Minor as Europe for the sake of this explanation).
In 1937, the Spanish "Civil War" lasted only 3 weeks, with a massive influx of German, Italian, French and Portuguese volunteers fighting for the Nationalist side, and none for the Republicans. After the war, Spain pressured Britain to give up Gibraltar. In return, Spain would allow British passage through the straight.
Belgium, being too critical to both the Netherlands and France, both nations then signed a treaty with Britain, making their "guarantee" on Belgium void. The Netherlands annexed Flanders, France annexed Wallonia, and Germany annexed Ostbelgien in the year 1938. The City of Brussels remains independent as the City State of Belgium, renaming the city itself to Belgium. The nation is similar to Andorra in how it is lead. There are 5 leaders. The prime minister of France, the president of the Netherlands, the Chancellor of Germany, the king/queen of the United Kingdom, and an elected citizen of Belgium. A large crime empire is based here, due to there being laws dictating that Belgium allow free transportation, with no border checks, into the Netherlands, France, Germany and Britain.
Germany annexed Luxembourg in the Franco-German war to try and break French defenses. After the war, Luxembourg remained German.
Czechoslovakia is still standing today.
During the Italo-Yugoslav War, Italy led a large army into Ljubljana, and began heading down to Sarajevo and Belgrade. Desperate for an end to the war, Yugoslavia signed the Treaty of Zurich, stating that Yugoslavia would grant Italy some borderlands in a straight line in Slovenia, and Italy shall not invade any more into the Balkans. As the Italian invasion was really just a bluff, and the army was weakened by the Ethiopians still, the Italians signed the treaty, with hesitance of course.
Seeing a weakened larger power with lands that you want means that you take advantage of the opportunity. Albania did this, and invaded Yugoslavia. The Albanian military was strong, and forced Yugoslavia to give up Kosovo and Montenegro. Albania still has those lands today.
Seeing Albania further weaken the Yugoslav army was something in and of itself. It was spectacular. Well, if you were a Bulgarian, or a Greek. Bulgaria and Greece both wished for Macedonia, and eventually it hurt their relations. In an attempt to patch things up, Greece offers Thrace, as long as Bulgaria helps Greece claim Macedonia in it's entirety. Bulgaria agreed, and both nations invaded Yugoslavia. Bulgaria took a few borderlands, but not much. Just a kilometer or two. Greece took the entirety of Macedonia. The kilometer Bulgaria snatched has been returned to Serbia.
After seeing Bulgaria go head to head with Yugoslavia and "still require Greek assistance" gave Turkey something. An ambition. Turkey performed a false-flag operation, and started a war with Bulgaria. Turkey was easily defeated though, as after the 3rd Balkan Wars, the Balkan Peninsula made an alliance. Instead of just Bulgaria, it was also Greece, Yugoslavia, Albania and Romania. Italy also joined in as well. After the war, the rest of the Balkans decided to grant Bulgaria the entirety of Turkish land in the peninsula, mostly so they do not have a repeat of the Second Balkan War. Again. After the 4th Balkan Wars disintegrated Yugoslavia, the rest of the Balkan Pact tried to get all new nations in the Balkans to sign the pact. The only Yugoslav nation that has not signed the Balkan Pact is Slovenia.
After the Breakup of the USSR in 1995, Abkhazia and South Ossetia became independent. They are now major Georgian allies. Armenia was granted Nakhchivan, and Azerbaijan was defeated by the Caucasus Entente, and alliance between Georgia, Abkhazia, South Ossetia, and Armenia. Azerbaijan is now a member of the Caucasus Entente.
After the Fracno-German War of 1940, Germany decided to stay still. Their war with Poland weakened them, plus a war with France? Devastating on the military. Eventually, Poland rose up and even took some lands from Germany, but at least Germany still has Ostpreussen.
The Breakup of the USSR let Russia keep Belarus.
The Baltic nations united, centralizing in Riga. Finland, after winning the Winter War with the Soviet Union, decided that they should be given Estonia, as Estonia was Finnic, like Finland. Of course, Balticia was not having it. Eventually, Ireland decided to mediate the situation. Ireland came up with a solution: Create a jointly-ruled nation, similar to how Andorra has always been, and how Belgium has been since 1938. In 1946, the creation of Finno-Baltic Estonia was accomplished. The King of Finland is one leader, the President of Balticia is the other.
Ukraine has declared independence from Russia in 1994, and tried to claim Ukrainian lands in Southern Bessarabia. Romania refused, and Ukraine still claims the land. The tensions between Ukraine and the Balkan Pact are high, and chances of war are high. In fact, it is thought that early next year, war will break out.