It’s fascinating the extent to which mercenaries played an enormous though underreported role in some of history’s most significant conflicts. I’ve been reading a lot lately about the history of Spain and the centuries-long reconquest of the Iberian peninsula from the Muslims by the Christians. The over-simplified narrative has always been Jihadists vs. Crusaders. But the truth is far more nuanced. You had periods when Christian mercenaries fought alongside Muslim emirs who paid well
You also have the celebrated 1683 battle of Vienna.
The Muslim Ottomans were besieging the Christian Holy Roman empire.
But, Christian France was an ally with the Turks. And the Calvinists among the Hungarians actually fought on the Ottoman side against the HRE.
On the othe side Sunni Muslim Lipka Tatars fought on the Polish side against the Turks.
Switzerland was created by Swiss mercenaries and their wealth.
To this day it is sometimes described as an Army that is a nation, but that was especially true in the past.