Discovering electricity
We’d still be using letters for communication, contruction tools wouldn’t allow us to build any structure more than 10 or so stories, spark is a key part of an internal combustion engine– so no cars unless you had a steam engine
The first primate to use another object to kill it’s prey.
There had to be a first one and other primates would have learned from it.
Realizing the special limbs and hands and feet they’ve inherited to grab tree branches were perfect for handling small objects they could use to get food would have marked quite a shift toward world domination.
The beginning of the roman empire
The Big Bang.
During thr Cuban missile crisis a Soviet submarine found itself surrounded by American destroyers and dove to avoid being detected, they lost contact with Moscow due to the dive and did not hear anything for a number of days. An American ship started to drop some practice depth charges which the sub believed were real depth charges. Two of the three senior officers believed that war must have started and decided to launch a nuclear tipped torpedo. Luckily unanimous agreement between the three senior officers is needed, and the third refused to agree, realising that they may have not been actual depth charges, he calmed the captain and convinced him to surface to reestablish contact. If it was launched it was very likely that it would have resulted in a global thermonuclear war. If not for this third man it would be a very different world we live in today.