"Полк" means "regiment". It's military unit. "Сосредоточить" in this case means "to direct against something/somebody". So "полки сосредоточив" means "regiments were directed against us".

Maybe this poem is about how (and when) Hitler attacked the USSR. That happened 22 of June in 1941 at 4:00 AM Troops were pulled to fight A peacefull shore. Nightless night was full of light, Then they started a dark war.