Mindset like WW2 Germany = Militaristic, Conquest, and self-serving. I did not include such things as what further was show, as I don't think even in the german ranks, all that was happening would remain. I am looking at the aggressive, invade/make war function of the "mindset". There is enough proof that even the soldiers of the German armies were appalled by the murderous acts of "Aryan selection" and the acts of mass genocide. I think eventually Hitler would have been taken down by his own soldiers, be it in the 1940s or 50 years later. I could have pointed at England or any number of other nations that had an expansion. So, let me restate this as Military/Conquest mindset.
With the introduction of atomic weapons, came the cold war, which was a war of fear of utter and total annihilation between the super-powers. But it didn't stop all the smaller countries from fighting, which is still happening to this day, and is did not stop conflict between even the super-powers. Korea, Vietnam, and even Afghanistan are the spoils of the super-powers conflicting with each other though out the length of the cold war.
While Eugenics and biological research is a potential issue, it don't appear to have taken place in the mirror universe. As far as I can see, there was no indication that the Eugenics war ever started in the mirror universe. So, I reason that the world stayed at a constant state of mass conflict. The Nuclear missiles and such still were built, but not used for a full scale attack, so Zefram still built his ship and such.
Ok, so since The US and a few other countries have nuclear weapons, that means stealth should not exist? Because having a bunch of nukes with no-one having a fool-proof shield against them is what this below implies...
Better Armor Vs. Better Fire power is a symbiotic evolution of technology
As long as one Side has the power over the other the one with the advantage will not see the need to innovate
If I am not mistaken, while just about any country can shoot down a handful of missiles, not a single country has a total shield to defend against it, not even Russia or the USA. The only "defense" is having the ability to destroy the attacking country as a "last act", total, utter, and mutual destruction. With ICBMs, there is a short period in which if one country launches a first strike with their nukes, then the other country(s) have a window to launch theirs. Boom Boom, everything goes up in flames, the end...
The question is, If a nation like China landed a million troops on US Soil (or reverse that, and the US invades china), would the US (or china in the reverse case) use it's ultimate weapon? I would think not... That would be the same thing if a spider landed on your leg so you use a 12 gauge shotgun to blast away the spider. So once again, the the ultimate weapon is useless. It would take lots of guns and troops to repel such an invasion.
With the Terran Empire, their goal is not utter destruction, but rather conquest. To conquer an enemy, you have to subjugate, as we seen proof of this in ENT and TOS with non-humans serving on-board the ships of the Terran Empire. So with the acquisition of the USS Defiant, they may have "the ultimate weapon"... but that is only a space born weapon of mass destruction. They still had the need to develop good tech to conquer entire planets. And using the "If you don't surrender we will blow up your cities and bases or even entire planet" threat does not make for a conquest to be successful. They still have to make the general population subjects/slaves of the Empire. For that, you can't just blow up every single city on every planet and colony an enemy holds. They still have to put troops on the ground and they still have to put down any resistance. The pain booths alone is not enough. It takes lots of weapons, and newer and newer weapons to make conquest effective as possible. This is our history, such as Rome. They had the "technological" advantage over almost every nation they conquered. However, they were expanding their empire, not just beating back invaders. They had to use lots of troops, and then they had to control the populations of the conquered planets, which required building an infrastructure to do just that.
So the way I see it, Sure, in the ENT days humans were more ruthless and self-serving. But with the introduction of the defiant, they expanded, probably too quickly, and before they knew it, with reverse engineering, they had reached critical mass by the beginning of the 24th century. At this point, a few small wins by the Alliance would have invoked disdain within the alien population (plus let's not forget Spock and his "change of mind" do to the TOS era encounter would sow seeds that ultimately brought down the Terran Empire) and thus caused a revolt. Reverse engineering a ship 100 years more advanced would have taken more than 50 years without dissecting the ship. Matching the production needs of the technology required years to build constitution class vessels. That is proven time and time again with modern technology (it takes a nation such as the US, Russia, or China at least a couple years to reverse engineer something of a foreign country, and then exploiting that technology takes an additional couple years). So it's reasonable to say that the technology gain from the USS Defiant would have been gradual. They would make a gain of advanced Technology only a decade in advance each at one time (repeatedly for the next 50 years or something there abouts) as they produced derived technology in the form of new starships. The Terrans only true advantage would only be found in mass production of slightly more advanced ships in any given timeline. That's why I believe the humans of the Terran Empire would have a huge research and development system, as well as a massive ship production capability. The Defiant did not give them their clear advantage, but rather, their drive for total conquest of the surrounding regions, which was driven by fear of non-humans (aka, xenophobia). It would be the critical mass point which allowed the failure of the Terran Empire.
Otherwise, if you argue they gained an instant 100 year advantage in the 2150s when they got the USS Defiant and they reverse engineered it quickly, then they would simply beat all enemies. They would have simply found they could not support an infrastructure of such a massive scale from total conquest and would have committed genocide everywhere. The Klingon/ Cardassian Alliance would never happen because all enemies, including planets and colonies, of the Empire would have been blasted to dust simply because they could not keep up with the demands of an empire spanning thousands of cubic lightyears. Remember, The Klingons are the first real enemy of the Federation. The Klingons didn't like Starfleet and sought to destroy the Enterprise... What do you think the klingons would have done with the Terrans? Thus, they could not make a direct attack because the Terrans had to have built a fleet quickly after Cochran captured the Vulcan ship. People forget, at the time, the Vulcans were one of the "superpower" races.
The instant gains of the captured Vulcan ship would be enough to build a fleet to defend earth for a decade or 2 Within 4 years, the Terran Star fleet is born. By this time, the Vulcans would investigate earth, and find a space-faring race. Again, I said before, the Vulcans are like the prime universe vulcans, and would be slow to think about attacking before trying to form a treaty of no-combat. But after that, the gains would have put the Terrans up to par with the Vulcans, Andorians, and Klingons, and the Klingons would have found themselves with a new enemy in their backyard. Only by having a sizable fleet could Earth defend against an attack by the Klingons... I do believe the Klingons of the Mirror universe to be just like the Klingons of the prime universe. This means they would have sent a fleet to attack earth by the beginning of the 22nd century. But by then, earth had to have a very sizable fleet with the same tech level of the Vulcans, and thus was able to keep the klingons at bay. After such conflict, the Terrans would see the need to grow and make themselves a force to fear, and so we see the Birth of the Terran Empire with the Conquest of Vulcan. With the Human's natural Fear of aliens justified, they would have committed the resources to quickly conquer Vulcan. And with the nature of Vulcans, they likely surrendered after a decisive attack by the Terrans was successful. So, after the Vulcans, the Andorians were the next natural Target, as the Klingon empire would have been huge compared to most any other known race or empire. The Klingons would from time to time, have to let the Terran Empire know not to mess with them. This would change quickly once the Terrans started deploying more powerful ships from the technology gains of the Defiant, as a single cruiser of the Terran Empire would then be a match for 2-3 Klingon battlecruisers by the 2160s. Now the Klingons find themselves on the defensive. It would take a couple more decades before the Terran Empire looked to the Klingon Empire to conquer, as the Klingon Empire would pose the biggest challenge. but Colony by colony, year by year, the Klingon Empire would lose ground to the Terrans. At this point, the klingons would likely get help from other empires, and most notably, the Tholians. The Tholians would be the only real match for the Terrans at this point. Likely, the tholians would not be involved with the Klingon's problems until enough gains were made by the Terrans to be a real threat to their borders. This new "mutual defense" ally would allow the Klingon Empire to survive the next 125 years until they had enough of the Terran Empire's growth. In the 2310s -2320s, The Terran empire would reach that critical mass I mentioned before, and so like a human bleeding while swimming in shark infested waters, there would soon be a feeding frenzy with many races and empires forming an alliance to deliver a final, crushing blow to the self-wounded Terran Empire. Planets, resources, and colonies would be split between the Alliance's races and earth would fall under the control of the Klingon empire, which also would have grown to double it's Prime universe's size.
Edit:
And yes, at the end of their Golden era, say sometime around 2280, their technology gains would likely be slowed, do to to much other things to focus resources, mainly their massive Empire's size. However, by this point, there is only the Tholians that can match the Terrans in firepower. Empires and races near the Tholians would survive conquest, but all other planets , races, and empires would fall to the Terrans. In this act alone, it would set back many other races, technologically speaking, by as much as 50 to 100 years.
Edit 2:
After the fall of the Terran Empire, the galaxy would experience it's first peace time since the Terrans launched their conquest campaign. this peace time would allow the races to relax their war machines, and thus their research would fall behind the prime universe's technology level by 20 to 50 years. Hence, once they build the Defiant class, the Terrans could quickly revolt and re-establish themselves... that's entirely a new question. Would they revive their old ways?.. Do not answer here, that is a topic for a new thread.
