Yes, ARMIES is a Scrabble word!

Letter values in Scrabble US: A 1, R 1, M 3, I 1, E 1, S 1.

Is it a valid word?

ARMIES is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

a permanent organization of the military land forces of a nation or state
a large number of people united for some specific purpose
the army of the United States of America; the agency that organizes and trains soldiers for land warfare

Also: regular army, ground forces, united states army, us army, u. s. army.

Not playable in Scrabble US: USA.