I want to know which non-judged Olympic event(s) is/are hardest for one country to dominate.

Which event has had the longest streak of different countries winning gold, with the streak including the most recent Olympics? (All different, not two alternating.)

(Also, is there a reason to believe a more recently introduced event is harder to dominate?)

Summer or Winter. Not including Paralympics, but I could post that as a separate question if it's interesting.