Answer based on context:

The Polish Army was made up of soldiers who had formerly served in the various partitioning empires, supported by some international volunteers, such as the Kościuszko Squadron. Boris Savinkov was at the head of an army of 20,000 to 30,000 largely Russian POWs, and was accompanied by Dmitry Merezhkovsky and Zinaida Gippius. The Polish forces grew from approximately 100,000 in 1918 to over 500,000 in early 1920. In August 1920, the Polish army had reached a total strength of 737,767 soldiers; half of that was on the frontline. Given Soviet losses, there was rough numerical parity between the two armies; and by the time of the battle of Warsaw, the Poles might have even had a slight advantage in numbers and logistics.Among the major formations on the Polish side was the First Polish Army.

Which army had about the same number of soldiers as the Polish army?
Soviet