Simplify the following text for a Grade 5 native English-speaking person.
Original: In addition , the 50,000 man Czech Legion , fighting on the side of the Allies , was now trapped behind enemy-lines , and was attempting to fight its way out through the east to Vladivostok along the Bolshevik-held Trans-Siberian Railway .
Simplified: In addition , a 50,000 man Czech Legion had been fighting on the side of the Allies . They became trapped .