Complex sentence: Governor Phillip was convinced the attack on McEntire had been unprovoked and that alongside other similiar attacks made against unarmed men in which some were killed or seriously wounded, believed that the natives had to be punished to deter them from any future attacks.
Split into simpler sentences: Governor Phillip was convinced the attack on McEntire had been unprovoked. There had been similar attacks against unarmed men in the past, in which some settlers had been killed or seriously wounded, and he believed that the natives had to be punished to deter them from any future attacks.