Because of that for any democratic government war is always a PR and popularity nightmare that almost always eventually takes government down in a disgrace.
In view of the above is near impossible to believe that in a dictatorship it is completely the other way around. Not only war does not increase discontent among the population, but it also actively reduces it. It works so surely and effectively that most dictatorships go to war not for any external reasons, but simply to solve the internal problems.
If that sounds too wild and unbelievable then try to explain why Iran-Iraq war happen in the 80s? War lasted a decade, a lot of people died, but border between two nations did not move an inch. Before the war nascent post-revolutionary Islamic Republic regime was in its infancy and could easily lose power. Saddam Hussain in Iraq also was far from secure. After the war, Iranian Islamic Republic could not be more entrenched and popular. Saddam Hussain also was secure enough to not fall down after failed invasion of Kuwait and decisive American retaliation during the Gulf War.
Both dictatorships were strengthened, not weakened by war.
However, why exactly dictatorships are strengthened by war. Are people who live in dictatorial countries any different from those of democratic ones? The answer is no; it's not the people that are different. The difference comes from the system itself.
Dictatorships are known for either not having any election or having fraudulent vastly rigged elections. That might give casual observer the illusion that dictators do not need to fear public opinion as they can always rig their way to victory.
That of course is an illusion. Revolutions of Spring of Nations and Arab Spring clear showed that public might rise up against the system and no amount of electoral rigging will save a dictator against such an uprising.
Because of the above, any dictator always cares about public opinion and being popular enough to survive. In fact, dictators actually care about being popular much more than democratically elected Presidents or Prime Ministers. In a democracy the worst that can happen to unpopular leader is that they lose the election, perhaps with extra disgrace of also losing their parliamentary seat. However, that is worst that can happen, fallen leader will continue to live in comfortable retirement and possibly write memoirs for extra income. In a dictatorship falling from power often means either exile or even a literal death, like in Muammar Gaddafi case. For a dictator it's their life that is at stake. They cannot afford being too complacent about popularity.
The fact that dictators cannot afford being unpopular leads towards the one thing that differentiates dictatorship from a democracy: censorship. Since cost of falling from grace in a dictatorship is too high a dictator cannot afford anything to tarnish their image. One guy criticising the regime or just complaining about prices can lead towards rather painful or even bloody downfall. That leads towards not only censorship but also a repression.
Overtime such repressions can get very brutal. Any scandal big and small can potentially be fatal. Thus, dictator will go to great length to suppress any information that can be detrimental to them keeping their power. The more desperate the dictator is, the worse offences he is willing to make if he believes it will allow them to keep power.
However, there is catch. The worse censorship and repression get, the more and more people grow to dislike the regime and dictator at the helm of it. Further escalation in censorship will lead towards even greater discounted followed by further escalation of censorship to keep lid on that discontent. It's a downward spiral with no exit that is bound to eventually lead towards all that discontent imploding on itself and taking the regime with it.
Facing the prospect of the imminent fall, a dictator will readily do anything to avert imminent end, no matter how insane it sounds. Even using nukes does not seem like a bad idea if the alternative is dying at the hands of rebels like Muammar Gaddafi.
That is where dictator often finds a solace and security in an unlikely place: war.
However, why population that was about to storm the presidential palace suddenly quiet down when war is called? Would not calling a war only make things worse? Would not media and public grill already unpopular dictator for such a wanton warmongering. No, because a dictator already destroyed all independent media.
In a liberal democracy freedom of speech together with independent media can keep government accountable. When George HW Bush announced that they will invade Iraq because Saddam Hussain had weapons of mass destruction, media and public questioned whether Bush lying or not. After the invasion media asked if any WMDs were actually found to verify Bush's reasons for invasion. Government could not produce find any WMDs or even prove they existed in the first place. As a result, media and public broadly denounced the war as unnecessary.
In a dictatorship such scrutiny is impossible. Media, already destroyed or severely damaged by censorship for reporting on various scandals of the regime, will not be able to hold government to account on war or investigate their lies.
That gives government near free hand to make up any fake reason for a war and expect public to just believe it. Unless a dictator completely stupid, they will be able to glue together a narrative where callous enemies attacked them first (or planned to attack them, but our smart leadership managed to make a preventive strike first), so the nation had no choice but to defend or be rolled over and slaughtered. That will force public to accept war as inescapable disaster they have to live through and do not blame government for that. Brits did not blame their government for the Blitz during WWII, they blamed Hitler. So long a dictator can convince their people their opponent is the aggressor, they will have such a free reign for a duration of the war.
However, why war? Why not just lie about something else instead?
That is not possible because most dictatorships fall due to internal problems. No matter how good you are at lying, public still sees the reality of life around them. When government keeps saying that life gets better and better while all people see around them is ever increasing poverty, misery and other problems, then eventually even people without much aptitude for critical thinking will start question the government. Especially when common people getting poorer and poorer, government bureaucrats and dictator themselves prosper beyond wildest dreams, like its typically happens in most dictatorships. In a dictatorship like that a sudden revelation that a dictator owns a luxurious palace or a superyacht can easily galvanise a revolution.
In contrast to that external problems are infinitely better for a dictatorship. Public cannot really know or see for themselves if a certain country X is really hostile and planning to invade them or not. That gives a dictator freedom to make up any lie and expect it to be believed by the majority at the very least. Most of the time they opt to a so called "besieged fortress" narrative: every neighboring country constantly plotting to attack them, only waiting for a moment of weakness to pounce on their prey. That narrative it then further spiced up by scenes of massacres and genocide that such potential enemy will enact upon the losers after their hypothetical victory. As a conclusion they simply add that these bastards from country X will not dare to attack us while our glorious leader is in charge but will definitely attack if one of his "weak and stupid" opponents will take power. Not every dictatorship that ever existed followed that narrative, by any that lasted did.
Public, that was constantly barraged by such narrative, can later be easily convinced that one of their "bitter enemies" attacked them even if in reality it was the other way around.
After a dictatorship have entered a war, they immediately feel many benefits. These benefits however can only last while war is ongoing, thus pushing dictators to prolong war for a long as possible even when everyone around them pushes for it to end. Sure, there is economic damage and possibly sanctions, but often these things cannot outweigh benefits.
Benefits of being at war mostly revolve around the war time measures that can be misused to deal with political opponents and discontent. Thanks to war every critic of the regime can be labelled as traitor who damages nation's morale and resolve in times of war. Even during peacetime dictators often label their critics agents of foreign power. However, jailing a critic for being an agent of hostile country X, when only a week ago you shook hands with president of country X as you signed a cooperation agreement will not look believable. Actually, being at war with country X will give such claims much more credence. "When at war you either stand with your nation or you are traitor." Dictators can easily misuse this principle to eliminate as many of their political opponents as they see fit. By extension they will wish to prolong the war as much as possible to keep access to this opponent removing "wartime" tool.
During war censorship can also be increased without any repercussions. No matter how traditionally restrictive country is, public will grow suspicious of every criticism no matter how justified is repressed for no apparent reason. Once again, such suppression of freedom of speech can easily be justified during war time. Government can eliminate every independent media outlet, citing protecting national military secrets. During peacetime public would be outraged but war somehow makes this acceptable in the eyes of casual citizen.
There is more. War enemies can further be blamed for economic hardships as well. During peacetime it is hard for government to deflect blame for country problems away from themselves. Sure, they can cite sabotage from hostile country X as reasons, but that further raises question of why police and national security fails to protect the country from sabotage. In contrast during war, all damage can be blamed on enemy. Lack of fund to repair road or build schools and hospitals, that is because they needed for defence. Even food shortages can be explained by war needs. Every problem, including those that had nothing to do with war can be explained with war needs.
Finally, war gives a good excuse to eliminate entire demographics, hostile to the regime. Most revolutions are done by young men. It is also young men, who serve in military. War gives dictatorship a good excuse to draft this demographic into military and then send them to die on the battlefield. War conditions make proving it was done to deliberately exterminate them is hard. Thus, thanks to war a dictator will easily be able to not only rid themselves of the people who would otherwise storm his palace, but also frame their death as an act of cruelty by evil country X.
All that makes war a dictator's best friend and protector. However sometimes war is simply not an option as all potential opponents are too dangerous. Then what?
One option is internal enemy purge where one accuses domestic opponents of being foreign agents and then prosecute them. All problems country faces are blamed on sabotage by such "agents" thus convincing public that these people deserve to be punished. However, blaming problems on internal "enemies" comes with expectation that things will get better once all such enemies are caught and brought to justice. Of course, jailing government critics will not magically fix roads or build schools and hospitals, forcing government to tap into other demographics in search for mythical agents who sabotage roads and schools. Eventually it will lead to absurd levels of paranoia, where every grocery store worker will be suspected of sabotaging groceries on orders of evil country X. Even when done very skillfully where every repressed group is thoroughly blackwashed until public is convinced, they are to blame, it still results in ever mounting casualties. Mao and Stalin with their multimillion victims can be used as examples of "best-case" scenario, if there is even a best-case scenario in something like that. Certain supporters of these two even nowadays insist that all who were persecuted under these two were actually at fault. At worst it will be like Pol-Pot in Cambodia, who tried to pull off the same thing, but did not convince anyone his victims did anything wrong and shortly after was removed from power by his very allies who installed him in the first place.
Alternative number two is Venezuela Crisis scenario, where country collapsed and no one trusts the government, but lack power to remove them. Not only Maduro's hold to power is as precarious as ever, but country and its economy and institutions have essentially disintegrated. Venezuela is essentially already a country in name only and that will only get worse the longer Maduro will stay in power.
One final alternative is for dictator and his supporters to flee and live in exile if there is a country that will accept them and will not hand them out to the new government.
Compared to either of these two options, a war does seem a lot more appealing to most dictators. That is why dictatorships almost inevitable will lead towards a perpetual war. The only world where dictatorship is stable is world of Orwellian 1984. every dictatorship moves humanity that much closer to Orwellian dystopia. That is why free world must fight to make dictatorships extinct.
