Technically we haven't been at war since (WWII?). Only congress can declare war.

In looking at this article from "Washington's Blog" it seems like they are stretching a bit. While we can debate almost endlessly about the definition of war and how it could be looked at, the conflicts given in this list and many of the others I've seen falsely equate basic military operations and basic security operations with all out war. If you hold this same metric to other nations, you'd be hard pressed to find one that hasn't done the same thing or been "continually at war" on some level. There will always be operations to safeguard a nation, and those are different from an all out war.

The list literally includes almost every conflict which involved more than a couple US soldiers on foreign soil.