unleash someone or something against someone or something
to turn someone or something loose against someone or something. The army unleashed a horrible attack against the enemy. Max unleashed his bullies against the helpless merchants.
unleash someone or something (up)on someone or something
to turn someone or something loose on someone or something. (Upon is formal and less commonly used than on.) The air force unleashed a bombing attack upon the enemy. The mob chief unleashed his tough guys on Lefty.