Could you elaborate your question? The Soviet Union was not properly established until 1922.

The Soviet Union wasn't around for WWI, the Russian Revolutions and the Russian Civil War happened during and after WWI, the USSR wasn't formed until 1922.

As for WWII, the only direct action that the USSR did that could've been interpreted as helping the start of WWII is the Molotov-Ribbentrop pact, signed August 23rd, 1939.

Stalin was very suspicious of the western powers treatment to Germany. Because of their policy of appeasement towards the Nazi government, Stalin, being the paranoid leader he was, feared that the allied powers would rather be accommodated with Hitler than ally the Soviets should Germany ever invade the Soviet Union.

This idea was further reinforced by the fact that the Stalin's repeated request for a formal alliance being denied every time he brought it up, including as recent as August 15th, 1939.

However, the real reason why the offers for the alliance were rejected was because Poland kept on refusing any alliance, fearing that an alliance with the USSR would cause for immediate hostile relations with the Germans and accelerate the war. The British and French could not force the Polish to accept the aid of the USSR or to formally recognize any alliance that could've been made.

At this point, it was well known to the west that this will end up being disastrous to them. Former Prime Minister and MP David Lloyd George even said "If we are going in without the help of Russia we are walking into a trap. It is the only country whose arms can get there.... If Russia has not been brought into this matter because of certain feelings the Poles have that they do not want the Russians there, it is for us to declare the conditions, and unless the Poles are prepared to accept the only conditions with which we can successfully help them, the responsibility must be theirs."

The Poles continued to refuse and the British and French governments weren't prepared yet to make the final conditions that Poland would have to choose or to be left to their own responsibilities, and the war broke out before they could be made.

Now here comes the Nazis foreign policy towards the Soviets.

Stalin had absolutely no interest in Poland, no claims he wished to pursue, no plans to invade Poland. Hitler, however, stated in March of 1939, his clear intentions to invade Poland had they not succeeded control of the Danzig Corridor to them.

Why did Stalin agree to this pact then? For two reasons, one is that it ensures peace between the USSR and Germany for the present and to officially expand the Soviets "Sphere of Influence", which, to Stalin, meant annexation to help further expand the Soviet Union to protect from the German Menace, the second point is beyond the scope of your question.

Yet again, why did Stalin agree to the pact? Defense. He didn't want to be attacked by the Germans without any allies to back him up.

Why did Hitler agree to the pact? Hitler was great at grand strategy and he learned from WWI. He knew a two front war would've been disastrous for Germany. He wanted to ensure that he could attack Poland safely, then invade the low countries and France, and presumably Britain prior to the USSR, keeping things primarily on one front at a time. It also isn't unthinkable that Hitler also anticipated Stalin to do something with his newly acquired sphere, whether be it annex, puppet, or complete exploitation, not only giving Hitler even more justification for attacking the Soviets, and also driving potential allies away from the Soviet Union due to their relative threat, discourage the Allied powers to take in the Soviet Union as an ally, and allowing the German army to capture cities annex by the Soviets with much more ease than historic Russian cities could have been some ideas he could've had in consideration when organizing the pact.

Now the very core of your question: Did the Soviet Union directly cause WWII? Directly, they did not. Directly, the cause of WWII is largely accepted to be when Germany attacked Poland.

What about indirectly causing WWII? Well, in August of 1939, Germany was fully mobilized, and armies were already deployed at the Polish border before the Soviet non-aggression pact, so it is very much in the realm of possibility that Hitler was prepared to invade even if the efforts to negotiate a deal with the Soviets doesn't break through.

Sorry this answer is so long! The prewar politics in Europe was anything but simple!

TL;DR version: the USSR didn't start the second world war, however there might have been things they were able to do to prevent the war or to lessen the extent of it.