* VFW requires foreign soil service (http://www.vfw.org/Join/Eligibility/)
* American Legion requires service during wartime
* Army & Navy Union USA and AMVETS require simply that one served honorably
These criteria directly relate to their ability to be non-profit VSOs in accordance with their charter.
Each of these VSOs also have subordinate organizations which one can join to allow support and participation in their local chapters.

VFW - Veterans of Foreign Wars USA
Veterans of Foreign Wars of the US is the official nonprofit service organization for USA military veterans benefits, VFW programs, community service, patriotic and world events, American flag sales, and services to military veterans and communities.

VFW - Veterans of Foreign Wars
We understand the unique bond you share with other veterans of overseas conflicts because we too, have been there. Since 1899, the VFW has been the nation’s leading veterans service organization in the fight to better the lives of all those who’ve worn the uniform of the United States military. No matter which conflict called you to service, we invite you to join us. Stand strong with the other 1.4 million members of the VFW as together, we...