In-universe chronological order of the Strangereal games, not counting minor conflicts shown only in subgames (e.g. AC5's Arcade Mode):
Air Combat/Ace Combat Zero: The Belkan War (1995)
Ace Combat 2 (1997-1998)
Ace Combat 04: Shattered Skies (2003-05)
Ace Combat 5: The Unsung War (2010)
Ace Combat 6: Fires of Liberation (2015-16)
Ace Combat 7: Skies Unknown (2019)
Ace Combat X: Skies of Deception (2020)
Ace Combat 3: Electrosphere (2040)
The real-world games (Infinity, Joint Assault, Assault Horizon) all take place in their own universes and do not have continuity with other Ace Combat games.
RL game release order: see Ace Combat