I am not american so maybe I am wrong but I believe it was Afghanistan in 2001 and Iraq in 2003 no?
The justification, weather correct or not, was in both cases exactly what you said. To “defend their own country”.
In Afghanistan to prevent further 9/11 style attacks from being committed against the USA and in Iraq to prevent WMDs from being used against the USA. The famous/infamous “do you want the proof to come in the form of a mushroom cloud?” bit.
Again, weather the justification was correct or not is not what I am pointing out. I am pointing out in both cases, the USA called soldiers to fight “to arms to defend their own country”