European countries had empires that spanned the globe
Africa
Asia
Oceania
the middle east
the america,s
even though they had soldiers at home with more casualities brewing often they would need more troops
Soo they used volunteers and conscripts
The british used the most colonial troops mostly from the indian subcontinent
Egpyt
And australia
The french were the second they used troops mostly from vietnam and Quebec
Heck even italy used some from libya and somalia