A few years ago there was a thread on the Axman and someone made a really keen observation: it was a 'mech designed for the previous war. And that got me thinking about what the Inner Sphere would look like without a Clan Invasion or at least one delayed by ten to fifteen years or more. And I think this takes on a lot of aspects for a potential 5th SW.
Most relevant to the game is where does technology and design go. Do battlemechs that are sort of maligned actually end up shining in a more level playing field. For example, does the Wolf Trap succeed as a light 'mech hunter and end up being embraced by the DCMS? How does the Axman perform against other heavy 'mechs when it doesn't have to fight Thors and Mad Cats? Perhaps we would not see designs such as the Bushwacker and battle armor development is severely delayed without the contributions of stolen Clan technology.
I imagine eventually 'tech advancement happens across the spectrum with the IS filling out the full roster of ER lasers, streak SRMs, and autocannon varieties. At the same time, would we be seeing weapons such as the heavy and light PPCs, PPC capacitor, or the light and heavy gauss rifles without the damage output and weight savings from Clan counterparts as a benchmark? Does some of the wackier tech show up? What about a weapon such as the binary laser cannon?
With all the recovered tech and new designs, I imagine warfare would be more intense than it had been in a long while. In retrospect, the 4th SW and War of '39 were relatively short affairs. Yet that doesn't even get into warships. Without the existential threat of the Clans, would ComStar be willing to share information and access to the large drives needed to move the warships?
And then the biggie would be politics and war!
The FedCom would be the side to beat, but I also imagine they would want to be gunning for the Combine after being humiliated in '39. When this war would happen is hard to say, but if it were not for the Clans then sometime soon after 3050. And with a less existential threat is Hanse Davion able to avoid a heart attack with less stress? What about Victor being stationed on Trell I and does he actually enter the war? In many respects, I would think that internal stresses of the FedCom would come to the fore depending on how the war goes -- eg. Free Skye, the Draconis March, rumblings in the Sarna March from Maskirovka -- all of which could provide a more reasonable pretense for a civil war if it were to happen.
The situation with the Combine would fall onto the enmity between Takashi and Theodore and how that plays out. Without the Clans and victories against them, Theodore might not have another clear opening to override his father. One thought I had would be if Theodore could somehow flip the script on the relations between Rasalhague and the FedCom. That would certainly be clever and unexpected. The FRR might not provide major assistance, but could stymie Lyran efforts into the DC. A major reversal of international relations could hurt the FedCom. Maybe ComStar is involved in changing allegiances between the DC and FRR. Which then gets us to ComStar...
ComStar's relations could tighten with the DC further and further providing the latter a much needed boost. However, if ComStar's bias were discovered the repercussions could reverberate throughout the IS. Does this land Theodore in trouble? How does the FedCom handle this? Would this be the downfall of CS and a different pathway to the WoB? Would the IS seize the HPG stations? Would CS tie the DC and FWL together in an alliance using leverage on "Thomas Marik"?
The FWL, however, might finally be in a spot to seriously participate in a 5th SW. Under the direction of Thomas, they have their economy in order and a strong federal government after the Andurien crisis. Perhaps a move to restore the Bolan Thumb could put a wrench in anything the FedCom would plan against the DC.
Finally, this gets us to the CapCon. And oddly enough, I think the CapCon is the safest of them all. Romano has basically made the CC a fortress. I do not imagine their neighbors would seriously consider attacking them outside of raids. However, I do not know if the CCAF is in any serious shape to attempt to conquer worlds. I imagine, however, there would be a serious shadow war between the CC and St. Ives. That shadow war could culminate in the same events of assassination or not. I do wonder if the ascension of Sun Tzu to the Celestial throne would delay or change what would become Xin Sheng. Perhaps the CC would not become so overtly Chinese (maybe Sino is the better adjective). Maybe there would be a reunification. Also, I think the new generation of house scions would not be so dismissive of Sun Tzu without an Outreach summit where he could put on an act for them.
To conclude, I think this would have been a fun alternative history to play in. I think I would like to see the IS powers actually get their hands on HPG tech. That was something being alluded to since the House Davion sourcebook. It would only make sense to finally get there. Maybe that could start a sort of Jihad event, but not to the same degree as we would see. But yeah, that is just me musing. Sorry if it came off a bit -- or a lot -- rambling and poorly proofread.
PS. The Periphery would probably stay as is. I mean, the Taurians are paranoid as always. What are you going to do?