The Basics on Combat in Civilization VI.
Combat Info
- Support Units (Settler, Scout, etc..) can now be embedded with other units, like anti-tank support with infantry, or a warrior with Settler. Note: These are units that are more sensibly depicted as special equipment embedded with a larger unit rather than standalone figures on the map. Also, similar units can also be combined to form powerful "Corps" Units.
- Corps are available mid-game and later on, three units can be combined together to make an "Army" and these Units can now be organised into a formation, which means they’ll always move together rather than having to be shuffled across the map one at a time. Formations can be applied to large collections of military units or civilian units and their escorts.
- Bombers can destroy Improvements and Districts with raiding.
- Combat experience goes into Military techs instead of promotions for Units.
- Barbarians can generate Scout, which in turn look for targets to harass, and apparently once they discover something of interest they'll often return with a larger force, since the Barbarians AI are much more intelligent and launch invasions based on scouting.
- Air Combat mechanics have been completely redone, but there are no specifics on which way so far.
Resolution
Unlike previous iterations of Civilization, it is the difference in 
Strength that determines the distribution of possible outcomes, rather than the ratio. A flat Strength therefore retains its value throughout the game.
See also: War