[The KG9 Kid]

And lose American citizenship for fighting in another nation's uniform?

No way.

[Alouette]

lose American citizenship for fighting in another nation's uniform?

You don't lose U.S. citizenship for fighting under another flag, even under an enemy nation's flag.

Johnny "Taliban" Lindh was convicted of treason, but he was not stripped of his citizenship.

During World War II many Americans fought in the Canadian and British forces.