Complex sentence: Their stand cost the Poles almost all of their ammunition and left them in a precarious position; lacking the means to intervene, they were forced to watch as the remnants of the XLVII Panzer Corps escaped the pocket.
Split into simpler sentences: Their stand cost the Poles almost all of their ammunition, and it left them in a precarious position. Lacking the means to intervene, they were forced to watch as the remnants of the XLVII Panzer Corps escaped from the pocket.