I second the Chaos March. I’ve run campaigns there alternating each week between two PC merc units. So Week #1, Savage’s Savages execute their first contract while the players from Berger’s Berserkers run the NPC opfor (militia, other mercs, FedCom, Blakists, Goons, etc.). Then Week #2, Berger’s Berserkers execute their first contract while the players from Savage’s Savages run the NPC opfor (militia, other mercs, FedCom, Blakists, Goons, etc.). Rinse and repeat until you’re ready to end the campaign. Then for their final contracts, the PC merc units face each other, augmented as necessary by allied forces to even the odds, in a knock-down drag-out fight. In this finale battle, I usually run a surprise Manei Dominion force that shows up after everyone is seriously damaged, forcing the PC units to join together if they want to survive, escape, and enter the next era.
The rough equivalent of the Chaos March in the ilClan Era is the Hinterlands, especially the Altima Mercantile League, which relies on mercs for its military (and produces all the new Falcon omnis). But unlike the Chaos March, the formation of the Hinterlands and AML has been comparatively bloodless and there’s not a lot of ongoing planetary conflict yet. You’d have to make some assumptions about conflict between the AML and the Horses, Jiyi’s Falcons, and others that may not follow the storyline going forward.
Three other good candidates in the Dark Age and ilClan Eras are the Wolf Empire, the FedSuns/Combine border, and the Arc-Royal/Falcon border. A grinding FWL campaign to retake the Wolf Empire seems to be in the offing. The Falcons and Kell Hounds/Wolves-in-Exile/Goons ground each other to dust in the Arc-Royal Defense Cordon for years until Arc-Royal finally fell and the Falcons moved on to Terra. And the Suns/Combine border has seen the Ryuken and Goons spend 3138 to 3146 taking over the Draconis Reach, launching deep raids to places like Glendora, and then rolling back the FedSuns military all the way to New Avalon.
Some other candidates from the earlier Succession Wars:
— Towne (1st Succession War) — The FedSuns take over Towne in 2783 with little opposition from the Terran Hegemony. But both the Combine and Confederation begin raiding Towne in 2785, and divisions between the FedSuns defenders split and hamper their defenses. Eventually the 5th Dieron Regulars invade in earnest, destroying the 56th Avalon Hussars and taking the planet.
— Hesperus II (2nd Succession War) — The 6th, 7th, and 8th Battles of Hesperus took place over five months in 2853 as Combine forces repeatedly assaulted the key military production planet. The factories escaped largely undamaged, but the Lyrans and Combine lost their last warships in this engagement.
— Caledonia (2nd Succession War) — Poor Lyran leadership led to slow bleeding of the elite 4th Royal Guards over a seven-year defense of Caledonia against Combine forces, ending in their final defeat in 2849. The Lyran agent known as Snow Fire assassinated the Coordinator in retaliation, leaving behind the 4th’s symbol before taking her own life.
Hope this helps.