The Molotov-Ribbentrop pact was a document about the USSR and Germany promise to do not attack to each other. How something can be annexed as a part of it?
The Ribbentrop-Molotov pact was a de facto alliance between Germany and the USSR, the Russians attacked Poland on September 17 and occupied its eastern part, and later introduced their troops into Estonia, Latvia and Lithuania. The Germans forced Lithuania to surrender one of its cities and a port. The USSR, having an alliance with Germany, also attacked Finland.
I would add Gdansk - it was a separate state - the Free City of Danzig - which was also occupied by the Germans in September 1939.
Germany invaded Greece at the same time as Yugoslavia, so it should probably be on the list. If we’re getting really specific, forces attacked Greece at 5:30 AM and bombers only started their missions into Yugoslavia around 7:00 AM.
On further research I guess Greece held out much longer than the Yugoslavian army so it lost earlier? So I guess if we’re going by date of capitulation the Yugoslavia is first?
I would add Gdansk - it was a separate state - the Free City of Danzig - which was also occupied by the Germans in September 1939.
Accuracy aside, there are actually many people who do claim Austria was invaded.