I'm delivering some leadership training at work, and came across this during my research

Origin
Late 15th century (originally denoting a military ploy): from French stratagème, via Latin from Greek stratēgēma, from stratēgein ‘be a general’, from stratēgos, from stratos ‘army’ + agein ‘to lead’.

So it would appear that 'Stratos' is the ancient Greek word for army, something which I had not known about before