A preventive war is a military, diplomatic, and strategic action taken to attack an enemy in the soonest possible time period to generate the greatest advantage. Prevention is when military action is taken against a target that is believed to have plans of an inevitable attack, even if it is not necessarily imminent. The concept takes its premise on the strategic belief that waiting and attempting to avoid war when it is obviously coming is dangerous and could lead to worse outcomes or greater risk. A state may choose preventive war in cases where the potential opponent of relatively equal or weaker military capabilities is evidently planning an attack. Therefore, striking first would start the military conflict faster but have the advantage of surprise as well as not allowing the opponent to get their forces and supply chains into position, providing a tremendous strategic advantage.
A preemptive war (or commonly strike) is the act of taking military action against an adversary when there is indisputable evidence of an imminent attack. A preemptive strike is typically used as a last resort when other options to prevent conflict have failed, and the decision to strike first is better than allowing the enemy to do so. In equal power conflicts, or potentially if the attacking state is weaker than their potential aggressor, a preemptive strike can potentially make the difference between victory and defeat, or at the very least, provide some early advantages due to its suddenness. A preemptive strike does preempt and limit an enemy’s capability to attack, but it is also high risk, as it both sparks the conflict and instigates the adversary towards potentially greater retaliation.
It may be difficult to tell the two apart because, essentially, both are first strikes against a potential enemy. The difference lies in the relatively subjective evaluation of the threat of conflict from the adversary. In practice, a preventive war also carries all the characteristics of a preemptive strike as well, meant to cripple the enemy’s capabilities to attack and gain strategic advantages in a conflict that is inevitable. At the same time, theoretically, it can be argued that a preemptive strike has the elements of a preventive war. Since waiting longer poses the risk of attack by the adversary or their further build-up of forces, risking a potentially bloodier conflict, a preemptive strike poses a lower risk and provides a strategic advantage.