Edit: The European theatre, in Asia the war started earlier when Japan invaded China. The most commonly understood start of WW2 was thebinvasion of Poland and the resulting declarations of war.
The narrative that USSR started the war, surrounding the "Molotov-Ribbentrop Pact" often misinterprets it as a partnership between the Nazis and Soviets to undermine the sovereignty of Central and Eastern European nations. Typically misrepresented as an "alliance," this controversial "nonaggression" pact, which included undisclosed provisions, was actually the culmination of a complex and urgent sequence of events. It's noteworthy that similar agreements had previously been established with Nazi Germany, such as Britain's naval arms agreement in 1934, and a nonaggression pact with Poland that same year. Additionally, it was almost exclusively the Soviet Union that took a stand against fascist forces in the Spanish Civil War two years later, offering support to the democratically elected government facing a fascist uprising, without the backing of other international powers.
Finally the infamous Munich agreement of 1938, where Britain and France agreed to the dismemberment of the last democratic and multinational state in Central and East Europe, Czechoslovakia, occurred without any consultation with the Soviets.
And no, the USSR did not start the war, that "honour" goes to Germany. The USSR did grap its portion of Poland so.
Regarding Munich, even worse, Czechoslovakia wasn't really consulted neither.
Edit: The war in Europe was ended by all allies, including the USSR. And that the USSR did most of the fighting, and dying outside the holocaust, should be crystal clear to everyone who ever read a short history of WW2 on wikipedia.
No, that was "the great war" that started with what's called "WWI" by many and ended with what's called "WWII". Basically, one big war with a really long intermission.
Worth pointing out that your view is still not mainstream.
WWI is well-known to have been kicked off with the assassination, though the whole thing was a powderkeg before that.
Re WW1: The assassination gave the Austrians the excuse to pose excagerated demands on Serbia. Because Austrian leadership, politically but especially military, wanted to conquer the Balkans. Austria got German support for those demands after Russia got involved on Serbias side, Germany was affraid a war with Russia was inevitable and would be unwinnable for Germany at a later date (history would proof both of these points correct).
Proof for the assassination being a welcome excuse, and not the reason: Serbia agreed to basically all of Austria's demands. Austria refused on basis of minor details, and the fact thatvthey needed an excuse. Back the day, formal declarations of war and acceptable excuses were still a thing in diplomacy, truely more civilized days in some regards.
After Austria declared war on Serbia, and launched its almost failed invasion, all the existing treaties kicked in: Austria and Germany declared war on Russia, France and Britain declared war on the central powers, including the Ottoman Empire, and events couldn't be stopped anymore. After all, everyone believen it would be a quick affaire, akin to the war of 1870. Didn't work out like that.
After the war, the German Empire was no more. The ancient guard and Prussian royalists were as opposed to the Weimar Republic as were the communists and Nazis (they came later). The result was a mess politically. When the conservatives failed to gain a majority in parliament, in part because society driffted away from the middle to the fringes left and right (immensly supported by mas media, radio, and Hitlers and the Nazis brilliant use of that as well as air travel, Hitler sometimes held two rallies the same day in different parts of Germany), they formed a coalition led by tze NSDAP. Conservative leadership hoped they could control the "Austrian private". They couldn't.
Which brings me to another myth: The Nazis were never led legitimate government. Truth is, they did. The first election on 1933 was in deed free and as fair as the other ones in the Weimar era. The fact that the NSDAP needed a coalition is normal, Germany was back the, and is today, a multi-party system. The times one party won a majority and not a mere plurality are extremely rare. Hence, the fust Nazi-led government was legitimate, they won that role fair and square.
The interesting, and today extremely important, part is thus: Once the Nazis were in power, they lost no time dismantling democracy from within. The next election the same year were the opposite of free and fair. The Nazis used their party apparatus, very well established across Germany, as a shadow govenrmwnt and administration. They used violence and every other trick in the book to manipulate the election outcome. It worked, they won a majority. And with that majority, their shadow party government and the additional powers assigned to the Chancellor, thay took power. When Hindenburg died, they merged the powers of Prwsident and Chancellor into the role of the Fuhrer, and their power grab was done.
The lesson of this being: democracies are a fragile beast, they can be attacked and destroyed from within if we are not carefull. And when this happens, well, the outcome usually is very, very ugly. Everybody should keep that in mind when they vote in 2024, regardless of where they are.
But yes, the overall cost in human lives was higher for the Soviet Union than for any other country or federation.