An important note about this trophy is that it can only be obtained during the
Cold War era. Go for this one
during your campaign or
start a sandbox game in this particular era and build an
embassy. Select the embassy and take actions to strengthen your relationship with the U.S.A. by praising them, sending delegations and/or form an alliance. As soon as your relationship reaches 100 end the mission by either completing it or failing it and this trophy will pop. You can select a mission by hovering over the red/yellow exclamation mark that appears above your palace and select it with
.
Credits for this method go to Playstationtrophies.org.