Does it sentence claim that if Poland wouln’t be left to fight a war on TWO fronts- they wouldn’t be defeated soon after?
No, it doesn’t. It states quite simply a) there was a plan between the Germans and Soviets to divide Poland in half, b) Poland was left to fight a two-front war, and c) after the two-front war began, the Poles quickly collapsed.
I would not read anything more into that than what’s above. If anything, the only “between the lines” comment that I see is the dig about Poland being “left” to fight a two-front war. And that would be a reference to the failure of France and the UK, both bound by treaties, to take forceful action on Germany’s western flank.
Polish planners had known long before the war started that they could not win a one-on-one fight with Germany. Plan Z – the Polish master plan for the defense against a German invasion, and the plan used in Sept 39 - was based entirely on this assumption. Poland’s strategic plan was to roll with the punches, to simply survive until such time as the western allies launched a counterattack in the west, drawing off German forces, and after which, Germany would the one caught in a two-front war. The treaties required such an attack in the west by a specific time line. For many reasons, the Allied did not launch a forceful attack. The Soviets invaded Poland the very day after the west failed to meet their “deadline.”
I do not believe the timing of the Soviet attack was a coincidence: Stalin waited until it was obvious the west would not or could not effectively intervene. I believe he had intelligence on the treaties’ time lines. IIRC, there was also a non-aggression pact between the USSR and Poland, which Stalin famously dismissed by saying Poland no longer existed as a nation. Poland, which had committed the bulk of its strength to fight in the west, was totally unable to meet the second invasion from the east, and collapsed.
Does it also claim that there were a simular war with USSR just like it was the war with GErmany?
I am not sure of exactly what you are trying to say here. If you are asking if the Polish fight against the Soviets was on par with the fight against the Germans, than I would again say no, the sentence doesn’t try to indicate anything of the kind. As I indicated above, the reality was the Poles had most of the strength committed to fighting the Germans. On paper, the Poles had a fairly large army (I believe at the time it was ranked as the sixth largest, either in Europe or the world, I forget which), but (because of pressure to delay from France and the UK) it was still mobilizing when the Germans struck, robbing them of a substantial portion of its manpower - I’m going by memory here, but I think they only had about 60% of their strength, and German action against rail and other transportation, coupled with combat losses, surely did not allow that figure to increase appreciably. The Poles had next to nothing left with which to resist the Soviet attack.
I hope that answers your concerns…