While military forces have been using impression and conscription to gather reluctant draftees for millennia, the word that most connotes the involuntary part to me is dragooned, especially as "dragooned into".
dragoon (v.): To force (into a course, etc.) by rigorous and harassing measures. (OED meaning 2)
to force into submission or compliance especially by violent measures (Merriam-Webster.com sense 2)
These days, you're most likely to hear dragoon used as a verb meaning "force someone to do something," like the way your best friend dragooned you into volunteering for the prom committee. Long ago, dragoons were soldiers who rode horses into battle and were trained to fight either on foot or on horseback. -- vocabulary.com
I got dragooned into building some wainscoting for my real estate company’s new office space. -- Reddit user "chainsawgeoff", 2021
Russian Federation (RF) authorities are dragooning Ukrainian citizens into uniform to fill gaps in ranks, but the unwilling soldiers often desert or flatly refuse to follow orders to attack, officials and news reports said. -- Kyiv Post, 2022
In your specific use case I might also simply and more generically say that the soldier had been coerced -- to compel to an act or choice ("abusers who coerce their victims into silence"), to achieve by force or threat ("coerce obedience") -- Merriam-Webster.com