While has many viable leaders for a Military Victory, Charlemagne ranks among the most powerful. He can amass a huge cavalry thanks to his Father of Europe ability, which grants two free Cavalry Units and gives all Cavalry Units +5 Combat Strength each time he enters a Celebration. Additionally, he can boost Happiness via Military and Science buildings with the goal of having as many Celebrations as possible. The civilizations that best enhance Charlemagne's ability are Persia in the Antiquity Age, Mongolia in the Exploration Age, and Prussia in the Modern Age.
Charlemagne should pursue Happiness in order to maximize Celebrations and offset any War Weariness accrued while waging wars across the Ages. Each of these Civilization choices also offers excellent Gold bonuses that Charlemagne can use to either strategically bolster his Army or develop towns/cities in more quickly. If it's available, the Lion Capital Memento synergizes very well with Charlemagne's focus on Celebrations, and, of course, Joyeuse, which provides +2 Happiness per Cavalry unit.
To get Charlemagne set up for Military Victory in , select Persia and start work toward the Pax Imperatoria Legacy Path by founding new or conquering existing Settlements. Charlemagne should prioritize Happiness output, utilizing the Military/Science building adjacency bonus for Quarters from his Father of Europe ability. Happiness is the driver for Charlemagne's Military success throughout the Ages, as it's needed for both Celebrations and to counter any War Weariness accumulated. Influence should be reserved to increase War Support for Charlemagne, and the Settlement cap should be increased as much as possible, all aiming to maximize Celebrations.
Charlemagne Antiquity Overview: Persia
Civics
Discipline, Spada, Satrapies, Organized Military
Techs
The Wheel, Iron Working, Military Training
Government
Despotism
Units
Immortal, Hazarapatis
Wonders
Gate of All Nations
Immortal units (the Persian unique infantry) also gain a
Read more on screenrant.com