During Vietnam, more than 30,000 Canadians (80 killed) served in the US military. During the early years of WWII thousands of Americans served in both the Canadian and British military. Thousands of Irish served in the British military and were shunned by theri government when they returned home.

The point I am making here is it is important "why" one serves, not where one is from.

Completion of military service earns instant citizenship for legal residents.