Valid arguments are advanced depicting Spain as a keystone to the Alliance; conversely, there are equally authoritative writings descriptive of her as a millstone to the West.
Dillon, J. G.
"Spain: Keystone or Millstone of NATO,"
Naval War College Review: Vol. 13:
6, Article 3.
Available at: https://digital-commons.usnwc.edu/nwc-review/vol13/iss6/3