Body armor has been used by armies since times immemorial .......
We see the romans, Greeks and other medieval and middle age armies sporting body Armour of various sorts......
I have rarely heard of body Armour used since the arrival if the musket. I mean soldiers in the 18th / 19th century, both world wars ... Korea ... Vietnam ....... 65 / 71 ... Kargil wars ....... I have not seen any type of body armour used by soldiers in these conflicts.
My first encounter with modern kevlar vests was during the American raid in Somalia ..... Now you see almost every western soldier an police officer equiped with one.
My question is were muskets/ rifles deemed too powerful to make any type of body amour effective OR were trenches, foxholes thought of as sufficient protection against all types of projectiles.