I'm interested in any historical examples people have of altruistic actions taken primarily to benefit future generations, which don't have strong positive effects for current generations. (So e.g. most climate change mitigation efforts wouldn't count, if we expect climate change to have a big negative impact on people currently alive - but maybe some do?)
Around 1800, five US states passed laws prohibiting the enslavement of future people (at least after they had reached a certain age) [1] [2] [3] [4] [5]. These prohibitions explicitly and exclusively applied to future people (operationalized as people born after X date, where X was shortly after the passage of the law).
More context and caveats: