He was involved in...
... Sabotaging peace talks that extended the Vietnam War by years. (This was literally treason and he knew it.) He did this to help Nixon win election.
... Carpet-bombing Cambodia (who weren't even involved) which gave rise to the Khmer Rouge (who killed a fucking lot of people).
... Using the Kurds as part of a proxy war and throwing them under the bus the instant he didn't need them any more (leaving them vulnerable to another genocide).
... Fucking Watergate. As in, he was in that shit deeper than Nixon himself and got off basically clean.
... Training and equipping the Mujahideen (as part of yet another proxy war with Russia) back when we liked Afghanistan (because they hated Russia too). They later became the Taliban. Lots of people say Bush did 9/11, and, while he isn't blameless, in a very real way Nixon and Kissinger did 9/11.
... Botching a kidnapping attempt (that was itself an attempt to prevent a progressive candidate from being elected in Chile) which ended up getting a famous general assassinated instead.
That's just what I remember off the top of my head.
It goes deeper.
Maybe as deep as his ass is in hell now.