The Polish army was strong for a country of its economical development - it was well trained and equipped with modern arms. However, they were unable to stand up to the full power of a grand power such as Germany, and even less the power of two grand powers (Germany and the Soviet Union).

The Soviet-Polish war and the Polish gains in it earned it the enmity of the Soviet Union. It already had the enmity of Germany due to existing partially on previously German land that the Germans wanted back. It also had the enmity of Lithuania, since it had annexed the city of Vilnius and the area around it.

Czechoslovakia and Poland also had a strained relationship, since Czechoslovakia had used the timing of the Polish-Soviet war to grab the contested area of Teschen from Poland.

Poland had friendly relations with Romania and France though.

As you can see from this, the Polish-Soviet war placed Poland in a strategic and diplomatic vice from which it could not escape. Once Germany and the Soviet Union came to an agreement, there was very little the Poles could do to change their situation.