30 Years’ War
The 30 Years’ War (1618–1648) was a continuous series of conflicts involving most European countries. It amounted to one of the longest and most destructive wars in modern history.
The conflict began as a war between Catholics and Protestants for the religious domination of the Holy Roman Empire, although political disputes were also involved. As the struggle continued, it turned into an escalation of the Bourbon–Habsburg rivalry (the rulers of the kingdoms of France and the Holy Roman Empire, respectively), which had simmered since 1516, and would ultimately continue to 1756.
Even as the quarrels that provoked the 30 Years’ War went unresolved, armed conflict ended with treaties in 1648, termed as a whole the Peace of Westphalia. This Peace also ended the hostilities of the 80 Years’ War (1568–1648), which was the Dutch war of independence from Spain.
These wars devastated entire regions: denuded by foraging armies. Famine and disease followed.
The armies involved, although not strictly mercenary, were expected to be largely self-funding. That translated in practice to pillaging the settlements encountered.