There are a bunch, for example:
https://en.wikipedia.org/wiki/Miracle_of_the_House_of_Brande...
It had huge impact on world history: it indirectly lead to German unification, it possibly lead to both world wars in the form we know them, it probably impacted colonial wars and as a result the territory of many former colonies, and probably also not their current populations (by determining where colonists came from and how many of them).
I'm fairly sure there were a few very close battles during the East India Company conquest of India, especially in the period when Robert Clive was in charge.
Another one for Germany: after Wilhem I died at 90, his liberal son Frederick III died aged only 56, after a reign of just 99 days. So instead Germany had Wilhem II as the emperor, a conservative that wrecked all of Bismark's successful foreign policies.
Oh, Japan attacking Pearl Harbor/the US. If the Japanese Army faction would have won the internal struggle and had tried to attack the Soviets again in 1941, the USSR would have probably been toast and the US would have probably intervened only slowly and indecisively.
I can't really remember many others right now, but every country and every continent has had moments like these. A lot of them are sheer bad luck but a good chunk are just miscalculation.
History is full of what-ifs, a lot of them with huge implications for the world.