Top 12
Let me explain my logic first. To me decisive means that there was more than one possible outcome, and the battle settled the fate of a conflict or the political progress of a nation.
1.Tsushima. The war had been won, but it prevented the Russians from the temptation of contesting the outcome, and turned the IJN into a major political player in Japan, creating the conditions that led to Japan daring to attack the US.
2. Marne. Prevented the Germans from winning in France in 1914, half responsible for the way WW1 was fought.
3. Tannemberg. The other half.decisive in the sense that if the Germans had lost there and in the Marne war could be over by Xmas.
4. Jutland. The way it went, it changed nothing. But Jelicoe really was the only man on both sides that could have lost the war in an afternoon. a major german win would have had massive moral implications, affected the outcome of the battle of the Atlantic in 1917.
5. Warsaw 1920. Prevented the Russian civil war from becoming the Russian revolutionary wars.
6. France 1940. The allies could have won, WW2 could have been massively different.
7.Stalingrad. The whole campaign, not just the final siege. If there was any
chance of the Germans winning in Russia it died there.
8. The battle of the Atlantic. The Germans did to little, to late. If Britain could have been cut off in 1941 it could have changed a lot.
9. Mukden 1948. The reds won. China went Maoist. World changing stuff
10. 1st Chinese offensive in Korea. The cold war got real. Proved that infNtry still mattered in the nuclear age.
11. Dien Ben Phu. Ended European imperial dreams. There were some hanger ons, but it sealed the fate of colonialism.
12. 1991 Iraqui war. Destroyed the concept of the large low tech arm as an option. Chinese wen high tech from then. Bombs got smarter. Every army in the world in a few years went pro and conscription seemed as old-fashioned as the crossbow.
Not included for lack of space he'll, let's make it 15!
Verdun highly misunderstood plan to make war so nasty the French would just gave up. 1917 strikes in French arm prove just how close it come to success. Had EvF plan Ben better understood and implemented, it could have worked.
100 days offensive in 1918. Made Versailles inevitable. The allies won fair and square and when that happens payback is a bich.
1973 yom Kippur war. Israel won the war but lost its mojo. The long road to peace followed, and from a military viewpoint it was downhill for the IDF. Lebanon 82 leading to the mess that was Lebanon 2006.