Franklin Mint – History of the US – Student Unrest Flares on College Campuses – 1970 – 45mm – Proof Bronze Medal – Mar 18-25 – U.S. mails delayed by first major strike of postmen – Apr 22 – Public awareness of environmental pollution is indicated by national observance of Earth Day – May 4 – Student opposition to U. S. invasion of Cambodia culminates in widespread protest and Kent State tragedy.