Treaty of Guadalupe Hidalgo, 1848
http://historicaltextarchive.com/sections.php?op=viewarticle&artid=141
"Each of the contracting parties [Mexico and the United States] reserves to itself the entire right to fortify whatever point within its territory it may judge proper so to fortify for its security."
http://historicaltextarchive.com/sections.php?op=viewarticle&artid=141
"Each of the contracting parties [Mexico and the United States] reserves to itself the entire right to fortify whatever point within its territory it may judge proper so to fortify for its security."