The Soviets spent a decade trying to form an anti-Nazi alliance, but the west was spending their time forming alliances with the Nazis, as well as nonaggression pacts like the later Molotov-Ribbentrop:

Meanwhile, Stalin had factories literally picked up and moved towards the Soviet interior, far from the German border. He had industrial production ramp up dramatically, and refused to have the troops muster on the border precisely because he was worried about the army being routed. He had everyone on high alert for a German attack, and was said to have obsessed even over bayonets.

The first few weeks went as everyone expected, the Nazis advanced quickly over largely open land until running face to face with the full industrialized might of the Red Army. Goebbels' diary is quite telling of the change in attitude. On the 22nd-23rd of June, the Nazis attacked confidently. On July 2nd, Goebbels wrote the following:

Overall, the fighting is hard and stubborn. We can in no way speak of a walk in the park. The red regime has mobilized the people.

July 24th:

We can have no doubt whatsoever about the fact that the Bolshevik regime, which has existed for nearly a quarter of a century, has left a deep mark on the peoples of the Soviet Union […]. It would be right, therefore, if we clearly informed the German people about the harshness of the struggle taking place in the East. The nation must be told that this operation is very difficult, but that we can and will survive it.

August 1st:

At the Führer’s headquarters […] they also openly admit that they were somewhat mistaken in their assessment of Soviet fighting power. The Bolsheviks are showing stronger resistance than we expected, and above all the material means at their disposal are greater than we had anticipated.

August 9th:

Privately, the Führer is very displeased for having allowed himself to be so deceived about the potential of the Bolsheviks by the reports [sent by German agents] coming from the Soviet Union. In particular, the underestimation of the enemy’s tanks and aircraft caused a great deal of trouble for our military operations. He suffers a lot because of this. We’re dealing with a serious crisis […]. The previous campaigns were a walk in the park by comparison […]. The Führer is not worried about the West […]. In our German thoroughness and objectivity we have always overestimated the enemy, except, in this case, the Bolsheviks.

September 16th:

We have totally underestimated the strength of the Bolsheviks.

This was not a walk in the park for the Nazis, because the Soviets planned for it. Modern historiography makes it quite clear that the Nazis and Soviets were never allies in any capacity, for any length of time, and were always conspiring against each other with no expectation of actual peace, just biding their time before what they desired to be a favorable start to war.