By making Cortes the Viceroy or Viceroyalty of Nueva Espana, Spain in effect put all the lands in the Viceroyalty under the control of the Spanish monarch at the time which was the King.
The Viceroy being Cortes, was simply a representative of the King of Spain and so ruled the territory on behalf of the Spanish King which meant that decisions made by Cortes carried the full authority of the Spanish Crown.
1. they finally joined the war because Germany embarked on a deadly gamble. Germany sank many American marchent ships around the British isles which prompted the American entry into the war
