Why wasn’t the NATO policy of an attack against one being an attack against all enacted when the Argentinian armed forces invaded the Falkland Islands which was legally a part of the UK? Why were firm allies of the UK such as the USA and some other members of NATO and the EEC reluctant to support the UK? Was it a case of world leaders supporting Argentina’s claim or did many support the British claim to the Falklands but preferred to stay out of it? And why did so many countries with no ties to Argentina or the UK support Argentina’s claim?
See this previous answer bu /u/Lilikoithepig https://www.reddit.com/r/AskHistorians/comments/6e48mr/why_didnt_the_uk_declare_war_on_argentina_in/
While more can certainly be said, I've written about the US involvement in the Malvinas war here.