Caption: Scottish soldiers serving Gustavus Adolphus (1594--1632), king of Sweden (1611--1632) during the Thirty Years' War (1618--1648).
These soldiers may be among the last of gallowglasses, a class of mercenaries of mixed Scottish and Irish heritage who flourished between the mid 13th century and mid 17th century (see Wikipedia: Gallowglass: History).
You will note that 2 or, maybe, 3 soldiers wear kilts and 2 are armed with bows and arrows: the arrows are in quivers. So even in 1631, firearms had NOT yet totally replaced the ancient weapon the bow and arrow.
The caption on the image insofar as yours truly can translate from German seems to say "in such fashion go the 800 in Stettin, who are called Irelanders or Irish."
Credit/Permission: Anonymous artist