Justice League of America No.100 "The Unknown Soldier of Victory."
Justice League of America No.101 "The Hand That Shock the World."
Justice League of America No.102 "And One of Us Must Die."
I've scanned the original cover of JLA 100 and the other large scans are of the original Australian editions, Super Adventure Comic Nos 62 & 63. (The opening issue appeared in SAC#61, however it was the final story and the cover was based upon the one from JLA99, which provided the lead story.) Small scans of the original covers are included below to enable a comparison.

The JLA/JSA crossover of 1972 was monumental in many ways: It started as a celebration of 100 issues of Justice League of America; It was the first to span three issues instead of the traditional two;  and it introduced the concept of teaming the two groups with a third set of heroes, in many cases revived from the golden age - in this case the honour went to the Seven Soldiers of Victory (or the Law's Legionnaires). The team of the GA Green Arrow & Speedy, The Star Spangled Kid & Stripesy, The Vigilante, The Crimson Avenger & The Shining Knight had not seen since their final appearance in Leading Comics No.14 in the Spring of 1945.

The cover scan of the Swedish edition of this comic was sent to me by Edvin Sandberg.  He has a magnificant web page on the Swedish DC comic Gigant, click on the scan to go to his site.