I am looking for Alpha Centauri-like PC games from around 1998 - 2008 I've tried one civilization once but I prefer SciFi but any help would be appreciated.

My PC Specifications: Operating System: Windows 10 Home 64-bit, CPU: i5-4440 @3.5 GHz (quad-core), RAM: 16 GBs DDR3, Dual Channel, Motherboard: Manufacturer Gigabyte Technology Model B85M-HD3, Monitor VP2770 27" Color calibrated IPS, GPU: NVIDIA GeForce GTX 780, Storage: SanDisk SSD PLUS 240GB (SSD), DVD ROM HL-DT-ST DVDRAM GH24NS95; External Blue Ray player, Sound Cards: Sound Blaster Audigy 5/Rx; Blu t Mouse: Logitech G HUB
Virtual Mouse, Network Card: Realtek PCIe GbE Family Controller (connected physically by ethernet cables). While I do pay for 100mbs (unlimited) and some shitty upload speed (Which doesn't seem to affect me), however, I think my desktops network card can only send/receive a total of 30mb/s.

In my opinion there is no other game that comes close to being as good as SMAC... old OR new, full stop.

Having said the above, the next best game will be Call to power 2.

I also loved civ2, civ3 is also ok.

Galactic civilizations 2 is fantastic... Galciv3 was good, but they messed around with it so much it has just turned to shit nowdays, ... but you can still get an earlier version working if you know how, in which case it is FANTASTIC!

I generally find that for all the newer games across the board, no one of them holds my interest all that much. It is always the case that the Attributes i like in any new game, are always outweighed by the aspects i dislike, and on balance, it is not sparking my interest all that much.

Couple of games i had high hopes for;

Planetfall - Meh
Pandora - Meh
Civ5 - At first i actually thought this was a great game, but that 2 unit tile limit kinda wore me down over time and i finally realized, this game sucks! Pandora has a 2 unit tile limit also, which contributed to the game feeling 'cramped' as well. I realize no one wants 'stacks of doom' but 2 units only?? One extreme to the other - F-ing stupid. Call to power has a 12 unit tile limit, but 6 would probably be fine.... but 2??!!! I don't know why they had to make it 2, ... f-ing stupid.
But the way Call to Power 2 handles units and armies is far FAR better than any civ game, old or new.

After civ5 i have not even bothered to buy civ6 and try it.

Pandora lets you stack units like you can in Alpha Centauri. I don’t think there is any limit on the number of units that can be on a same tile.