I would list 3 battles that would have made our history be much different if their had not the same ending...
1) Battle of the Yanagi Cloud: thats when the GMG practicaly finished off the remainder of the rheinland navy, virtualy ending the 80 Years War. That led to the end of the Empire a couple of decades later.
the other 2 are connected...
2) Battle of Tohoku: when they killed Tekagi, and started turning the tide on the Nomad War. and
3) Battle of the Dison Sphere: that was all or nothing, mankind would be in extinction by now if they had lost that one.
Something something, Battle off Samar, something something, Japanese Center Force, something something, entire Allied operations in Pacific endangered.
No one's touched the Spanish Armada? Would have changed European development for the last 500 years entirely! All thrown out the window over a storm! Tough luck!
Now I am wondering what would history look like if Polish-Lithuanian Commonwealth, instead of fighting off Turks // Ottoman Empire in Battle of Vienna (1683), negotiated with them.
But I believe there wouldn't be Russian Empire if Poles treated Cossacks way better than they did (what lead to Chmielncki's (Khmelnytsky's) Uprising). Well, perhaps it would even create Triple, not Double, Commonwealth with Cossacks. I believe this was the major No up of Poland in 17th Century (since king had no real power, but Nobility could pass of block anything with their veto).