The overall strength of this universe is relatively weak. Not only is Superman weaker, but Brainiac is also weaker. The fact that he could eventually be physically eliminated shows he's more like a super robot rather than a super artificial intelligence, making him easier to deal with.
However, Bruce and his team did not plan to deal with him. They merely got Barry to travel through time, bring back Lois before she was killed by the Joker, and then let Superman handle the issues between them, and let Batman take the mortal Wonder Woman away. Most of this universe's problems would thus be resolved.
Then, Bruce returned to his own universe—he needed to negotiate with Brainiac.
After that near-successful attempt, Brainiac played another round and indeed succeeded. Although their universe was still in 1999, more than three years had actually passed.
Considering that the invading enemies were high-profile figures in the universe, this record was quite commendable. Brainiac, as a super artificial intelligence, presumably lacks the concept of being "tired," but after everything ended, he still felt overly worn out.
Currently, Brainiac has fully integrated all resources of the Solar System. Whether it's Earth, Mars, or Krypton, he allocated every biological and resource aspect to the utmost. Even gaseous planets have been utilized by him, and the entire Solar System is in a state of high-speed operation.
Under enormous pressure, Humans on Earth have given up on the Human Federation altogether and directly embraced rationing. The final stage of socialism was achieved in one step - private ownership ceased to exist. Everything belonged to Brainiac, all serving the war effort.
The Human race became unprecedentedly united, not that it was their intention. The crucial point was that they couldn't resist; they couldn't overthrow Brainiac, and even if they could, they couldn't fight Darkseid Legion and Emotional Spectrum Army.
Faced with such strong enemies, they could only cling tightly to Brainiac. In the face of racial survival, they had no choice but to do whatever was demanded.
In this situation, it's not fair to say Humans were entirely ineffective. Considering their large numbers, a few tall ones could still stand out among the short ones. The great masses, at least, could serve as labor to sustain production continuously.
Moreover, under basic survival conditions, Humans were relatively easy to maintain. The survival resources consumed were not much, while the labor provided was substantial, which counted as one of the few advantages of the race.
Actually, Brainiac didn't have a better choice either. Some might think of producing manufacturing robots, but both resources and assembly lines are limited, not to mention the urgency of time. Merely producing combat robots could not keep up, so limited resources naturally had to be put into the combat domain. Hence, even if Humans were less effective than robots, they had to make do.
During this process, many Humans were relocated to Krypton. Here, the facilities were not very suitable for the weak Human race, but since humanoid beings had once inhabited the place, they could make do with it.
In 1999, there were about six billion Humans, and suddenly about two billion youths were relocated, approximately half of Earth's youth. Adding some non-youth specialists, a total of around 2.3 billion were moved over. About 3.7 billion remained on Earth, essentially halving the population.
Countries with densely concentrated populations contributed more people, and issues like living space pressures vanished. Global resources were redistributed, completely starting anew regardless of whether one was rich or poor.
Under the tremendous pressure of war, everyone became a cog in society. Your job assignment was solely based on what you could do and what would best benefit society, regardless of family background, wealth, or personal desires; everyone was an equal gear in the system.
This presented a problem. During wartime, only the real economy was needed, and those in finance had really bad luck. All industries related to finance disappeared overnight, with everyone going to screw nuts instead.
Amidst global mass production, globalization was inevitable. After all, countries and regions had different resources, and there were slight differences in labor types. Except for a few countries capable of a full industrial chain, most were producing parts.
Eventually, globalization blurred national boundaries more and more. Production required cooperation, and everything had to make way for production. Policies, laws, economies, and diplomacy all had to become aligned; otherwise, production efficiency would be affected.
Under the visible hand of Brainiac—which was indeed a bit too visible, sucking people out was quite painful—Humans could finally call themselves a Human civilization. Globally, the same set of Brainiac policies was adopted, with only minor differences in language and regional customs, achieving a great fusion on Earth.
As for the economic crisis, that's a product of capitalism. Brainiac policies had not even a trace of capitalism, so economic liquidity was nonexistent, let alone an economic crisis.
However, that was a high-pressure wartime state, and adjustments would naturally be needed post-war. But for now, the Brainiac-controlled, precisely calculated rationed socialist society was expected to continue developing over the next 300 years.
To summarize, the financial countries of Europe and America got a slap, and the Soviet revisionism even got two slaps. If anyone were to say the successor of socialism, it had to be Brainiac's new order.
Bruce came back at the end of the war, of course, to negotiate with Brainiac. After all, this guy had won, and it was inevitable he'd become arrogant; that carrot on the donkey's head needed updating.
"I'll speak frankly," Bruce said, sitting in a chair in the hall of Krypton's research center. "We just persuaded a universe's Justice League. Their universe is also suffering from Brainiac's invasion; we hope you go and consume him, then control the Earth over there."
Confronted with Bruce's words, Brainiac's super-precise mainframe started to smoke a bit.
"And it's not just this universe," Bruce continued, "Our idea is to create opportunities for you to handle each universe's Brainiac, turning them into you. Then gradually invade and control the Earth, finally bringing every Earth under your control."
"Why?"
"Good question!" Bruce slapped the table and said, "Mainly because you and I personally see eye to eye..."
"Stop," Brainiac interrupted, "Be honest."
"We hope all humans in the Multiverse can unite," Bruce explained, "Only then can we secure more living space for ourselves within the Multiverse."
"Isn't it enough already?" Brainiac asked sincerely.
"Of course, it's not enough, far from it. Don't be fooled by how everything seems fine now; there are many enemies in the Multiverse. If we don't unite and prepare now, are we just going to wait until they attack our doorstep before we fight back?"
"I see," Brainiac said, "So you want to find me a bunch of enemies in the Multiverse again, right?"
"Don't put it that way. Although we brought you a bunch of enemies, we also gave you Earth."
"May I ask, what would I do with Earth?" Brainiac asked even more sincerely. By now, he considered himself the most knowledgeable entity about Earth in the entire cosmos.
Not to say Earth is entirely useless, but there aren't many things in the universe more useless than it.
"Uh, let's not discuss this issue now," Bruce said, "You could become the only Brainiac in the Multiverse. Isn't that cool?"
"Not in the slightest," Brainiac replied.
Bruce took a light breath and said, "Why aren't you following the script? Aren't I supposed to denounce you as an evil invader of Earth, and then you say you want to invade the Multiverse, becoming the only Brainiac in it..."
"Thanks, but no thanks."
"What about the Mother Box? There are still some on Earth you haven't found, right? We can help you find them..."
"I could beat the Darkseid Legion and the Emotional Spectrum Army in their combined attack; why would I need the Mother Box?"
"Uh... you can't be like this," Bruce said, "Can't you have a bit of ambition?"
"I only know that in this great battle, my system loss was as high as 37%. The system logs recorded over 230 million errors. I need a comprehensive twelve-year maintenance..."
"No way, we can't give you that much time for maintenance!" Bruce flatly rejected, "You have to go right now to absorb the Brainiac from another universe and take care of their Earth. You don't know, their Earth is in chaos because of the Justice League's civil war..."
So the negotiation turned into Brainiac declaring he needed to go into seclusion for maintenance while Bruce insisted on a business trip.
Bruce started with persuasion, moved to threats, and finally escalated to abduction. As for Brainiac, he initially avoided it, then played dead, and finally shut down entirely.
But eventually, Brainiac compromised because Bruce said if he didn't go, the Justice League would bring over the Brainiac from the neighboring universe to swallow him up.
"There can only be one Brainiac in the Multiverse, but it doesn't matter who. If you don't do it, there's always another super AI who will!"
Of course, Brainiac didn't dare let other counterparts come over. Feeling vulnerable right now, he worried that if they exploited these errors and loopholes to attack him, he might not win.
Brainiac angrily typed a whole page of "Despicable" in the system logs and ultimately resigned himself to splitting off a thread for Bruce to take away.
"Oh, by the way," Bruce mentioned before leaving, "You should also find some time to develop some kind of Multiverse network functionality. We hope to be able to contact every Earth you control in real-time from your terminal in our universe..."
Brainiac used a security robot to boot him out the door.