Original: The term wehrmacht is in Article 47 of the 1919 Weimar Constitution, establishing that: Der Reichspräsident hat den Oberbefehl über die gesamte Wehrmacht des Reiches ("The National President holds supreme command of all armed forces of the nation").
Simplified: The conscription law introduced the name Wehrmacht, so not only can this be regarded as its founding date, but the organization and authority of the Wehrmacht can be viewed as Nazi creations.