A defensive alliance curiously not invoked when the Soviets did supposedly "invade." I wonder why this was so?
1) Because Germany also fought against Poland and Romania did not want to be at war with Germany and was not even obliged to dos.
2) Because Polish authorities issued an official note in which they "released" Romania from her obligation soon after the Soviet Invasion.
and decided that going it alone was better than accepting the truth and seeking the protection of a larger alliance.
But wait, this is actually what Poland did - Poland did not go alone, but accepted the protection of two larger alliances - France and Britain.
France at that time was considered (wrongly - but it only turned out in May and June 1940) as the strongest military in the world.
And Britain ruled the seas and ruled the airs (this was also not entirely true, but it also turned out later).
You know, like the alliance the Soviets had been seeking for three years.
The Nazi Germany was as well seeking alliance with Poland (an anti-Soviet one) for several years.
And Poland refused both offers. At the same time, Poland was trying not to get invaded by either of these two powers.
As I already wrote before, the main line in Polish policy was the policy of "neutral balance" between Germany and Russia.
You would have put the Nazis at the gates of Belarus almost without a fight!
When the Ribbentrop-Molotov was signed on 23 August 1939, it was already more than obvious that Poland was going to resist.
So your statement that Soviets were at risk of Poland accepting Germany's demands and not fighting, is wrong.
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Oh - we might add that Poland started to ask the Soviet Union for support (but in the form of selling and sending weapons and ammunition, rather than sending troops) in September 1939. The Soviet Union never provided a clear response to those requests, and several days later it invaded Poland.