1) Thirty Years’ War: Ended in 1648. Let it go.
2) World War I: Germany bears most of the blame for starting WWI.
The largest share of responsibility lies with the German government. Germany's rulers made possible a Balkan war by urging Austria-Hungary to invade Serbia, well understanding that such a conflict might escalate. Without German backing it is unlikely that Austria-Hungary would have acted so drastically.
https://www.historylearningsite.co.uk/world-war-one/causes-of-world-war-one/causes-of-world-war-one/#:~:text=Germany%20has%20been%20blamed%20because,go%20with%20the%20popular%20mood.
In July, 1914, Germany gave Austria a "blank cheque" in handling its punishment of Serbia regarding the assassination of the heir to the Austrian throne. It meant that Germany would support whatever decision Austria made. Austria decided on war with Serbia, which quickly led to escalation with Russia...
Shortly after the war began, the German foreign office issued a statement justifying the Blank Check as necessary for the preservation of Austria, and the Teutonic (German) race in central Europe
https://en.m.wikipedia.org/wiki/German_entry_into_World_War_I#:~:text=Germany%20entered%20into%20World%20War,capture%20Paris%20from%20the%20north.
3) World War II: correctly labeled "Hitler's War." 'Nuff said.
If Germany and Austria suffered devastating population losses in the 20th century, it's their own fault. German-Americans did their part by fighting against the Kaiser AND the Fuhrer. Let's all celebrate that.