A group of young soldiers finds themselves in a world of doing the worst crimes of mankind.

For one part, the logline feels incomplete because lacks the consequences or at least the stakes.

For another part, it has redaction problems. "In a world of" is doesn't makes sense and it doesn't add information.

And finally, the protagonists need a strong adjetive that gives them character. Ex. Rebels, lunatics, religious, etc.

Examples to correct the prompt would be:
A group of young soldiers finds themselves in a violent war in the gaza strip doing the worst crimes to mankind in order to defend the honor of their nation.

or

A group of religious young soldiers finds themselves doing the worst war crimes questioning if they are really the good ones despite following their God's commands.

Overall, you need to give more information about the character, the type of conflict, what is a stake, the possible consequences and the reasons behind their actions.