This stems from two personal anedoctes (I know, personal anedoctes... but I am not using them to support an argument). I have a portuguese friend whose surname is "Lalanda", which he knows for a fact stems from having an ancestor fathered by a French soldier (Laslandes) during the Napoleonic War. Another one has the surname "Grou" and it can only be traced to the same time and to the area where the English had their base of operations, which we (half-joking) theorize to originate in the english surname Grout / Groutt. So, taking into account that Portugal was peripheric during these years, much larger movements have happened somewhere else in Europe. My question is whether or not are there any known populations that can be traced to those said armies?
In the Low Countries -- today's Belgium, Netherlands, Luxembourg, and even parts of France -- there are groups that identify as descendants of Spanish soldiers. They call themselves sinjoor, from the Spanish word señor.
They came due to the Eighty Years' War, which ending ran concurrently with the Thirty Years' War.
It's quite alright here to ask a question based on an anecdote. Unfortunately I can't answer this for you, just want to clarify the rule.