Not an expert, but just a casual history fan...

The Great Turkish War had the famous Battle of Vienna. The Ottomans had Vienna under siege until the Polish Hussars showed up. They were the elite fighters, selected from nobility, they had the money for the best gear and best training. They had very flashy outfits, banners, and wings!

Three thousand Hussars lead a group of 18,000 mounted cavalry to swarm the Ottomans, breaking the siege, saving Vienna, and started the string of defeats for the Ottoman Empire losing much of Hungary to the Holy Roman Empire.

I can't begin to imagine the sound of 18,000 charging horses, what shock that would put into a soldier that thought they had almost won a great victory, and how frightening it would be to see 3,000 winged special forces in heavy armor bearing down on you.

Here is a historic representation of a Hussar and a modern reenactor.

Other than that, World War I came at such an intriguing time. All kinds of new weapons appeared from gas weapons to tanks and real machine guns and automatic rifles and pistols. Meanwhile, people are still trained in cavalry charges, bayonet fighting, carrying swords, and firing single shots. It began the world's change to modern warfare. So much became outdated in the course of a few years, and where we are today really began here.