Is the galaxy doom to be this way always at war?
Strange as it may seem given the news we usually hear, IRL the world right now is the most peaceful it has ever been - people kill each other less than they ever have, and civil rights of varying degrees have been extended across racial, gender, religious, sexual orientation, and class lines in most of the world to a degree never before seen; in many places, including most of the West, lesser rights have even been extended to other sentient animals. This trend has been a fairly consistent one across the arc of history, as civilizations progressed both technologically and socially. So why don't we see something like this in Star Wars?
Well, for one, the writers like to write conflict in a medium called "Star Wars".
But let's stick to in-universe explanations, but viewed through the lessons of reality. I tend to think there are two main factors at play:
1) The Force. In reality, one person may be stronger than another, but only to a point - in Star Wars, that point doesn't truly exist, as you will have one person with the sheer physical and mental power of millions or billions, able to annihilate them with his mind alone. Superpowers being possessed by individuals throws off the balance of power that helps regulate normal interactions between various beings, as well as instilling a sense of superiority in the wielder of such powers when compared to those who lack them; just think of the various comic book universes with superheroes and how rarely they find long-term periods of peace and happiness for all. Throughout history, as the power of the state to regulate violence within itself has grown, that violence has diminished because no matter how strong you personally are you can't take on the cops or the army by yourself, and they will remain a check on your actions - but this does not apply to a sufficiently powerful Force-wielder. Add to this the personally corrupting and addictive effects of long-term use of Dark Side powers, and you have a perfect recipe for brewing beings that will constantly throw society into upheaval.
2) Stagnation. Both technologically and socially, the galactic society has been almost exactly as it is for thousands of years. If anything changes technologically, it is usually not some new invention but some old tech that has been lost over time and is rediscovered, such as cloaking devices or cloning. But in reality, technological growth has been a constant driving force behind social changes, especially communications technology - and in Star Wars there is no true technological growth. The GA fought the Vong with pretty much the same technology that the Old Republic fought the Great Hyperspace War with: hyperspace drives, blaster weaponry, energy shields, holocommunications, combat droids of equivalent complexity, etc. And the social situation largely reflects this stagnation: with the exception of the Imperial period after Palpatine converted the Republic, for 20,000 years the Republic had remained largely democratic (at least at the intersystem scale), with democratic norms such as freedom of the press, abolition of slavery and legal equality between species, religious tolerance, etc. While these aren't bad social norms, they also don't really change except for some small periods of regression to less civilized norms, most notably the Imperial era under Palpatine, which then are largely bounced back from - there's no progress towards a yet "better" society, no sense that rights are continually being expanded to those that deserve but do not yet have them (such as droids, for instance, whose rights largely remain unchanged for millennia).
In short, they're not learning and improving socially, so whatever structural problems the society has are going to continue to express themselves at intervals over time, usually in the forms of civil war or other social upheaval. Those upheavals tend not to last, and the democratic norms reinstate themselves across most of the galaxy, but they cause a lot of damage before they're done.