There is a common trend of young men being interested in the Roman empire out of movies and populat history, and imagining it as a militaristic, right wing hyper-masculine empire that was great for men. Spartacus, Rome, Gladiator... to different degree all give a perception of Rome being a sort of warrior-culture, sometimes bogged down by decadence. Gladiator II takes this to a ridiculous extreme. For that particular movie, I recommend reading Brett's, from acoup.blog, critique:
They have an impression that Rome was somewhere on the left-right wing linear spectrum we have in the United States and that they were most likely on the conservative side. Very much religious, patriarchal, warrior-oriented. The thing is, compared to today, majority of previous societies were that way. If we want to understand why Rome was so succesful, we need to compare it to the societies it defeated and/or assimilated. And surprisingly, we will find they were far more liberal and progressive than the rest. Rome was not humane by our standards. The more useful question is why it scaled and lasted in ways that Sparta, Athens, Gaul or Carthage did not.
Sparta should have never existed
Sparta is the easiest contrast because its political order was built on closure. Its citizen body was small, its military discipline was extreme, and the helot system was central to their society. It was the basis that let the Spartan elite live as a permanent warrior caste, elite in their own perceptions. A society organized around ruling a large, subordinated population by force can be formidable and it can make you feel like you would have had a blast... living as a Spartiate. Well, not really. Shortly after implementing this system (in historical terms) Spartans started running out of, well, Spartans. The society was very elitist, you could only lose your status and move down the hierarchy, not up. Helots would never be spartans and, even those that would help in critical emergency and exceed in battle would end up getting slaughtered due to being a risk to the status quo. What kind of incentive is that for anything? Bret's deconstruction of Spartan society is a masterpiece and it's best to just point it out here:
In a nutshell, Spartan policies ended up reducing number of Spartiates, with no advantage in terms of military effectiveness (they lost against other Greek policies as often as they won), created no art or even military fortresses and had very little achievements in terms of innovation, even warfare related (such as siege material, fortification or naval infrastructure). The Romans mopped the floor with them in their warfare, exceeding them in battle with superior techniques, logistics and infrastructure. All of that came from having a society that values thought and diversity of skills, rather than only glorifying the warriors, such as Sparta did.
Athens is harder for modern readers because it tempts admiration first. Its civic culture was there, and so was its democracy, theater and other civilian. But the civic core was still narrow. Women were outside the political body (far more than in Rome, where they were at least able to act in the background) and mostly ignored. Metics (non-citiens) could live, work, and matter economically without entering that body politically, without having any impact. Athens could be brilliant and still keep citizenship restricted. There was a very small circle that you needed to belong to to be able to influece the city and feel part of it. In the Roman empire, however, we have plenty of emperors that descend from slaves themselves (Diocletian, for example). Inclusion is not the same thing as equality, and Rome's advantage was not equality. It was a wider capacity to make more people count as Roman over time, making people feel part of it, rather than outsiders. Social mobility, for the times, was one Rome's advantages.
Roman mobility
That is where Rome looks different. Roman belonging expanded through law, service, office, alliance, municipal status, manumission, and eventually wider citizenship grants. Rome had more institutional ways of binding outsiders to the system by giving them some stake in it. That mattered. A polity that can turn allies, provincial elites, auxiliaries, and freed people into some recognizable form of insiders has an easier time turning expansion into continuity.
The Roman Empire is often used by right wing advocates (originally, even Mussolini) to justify fascistic tendencies. Yes, if we compare to modern societies, Roman mindset was very conservative and war-oriented. However, that was common everywhere. Rome won over most of these other states and incorporated them effectively into their empire because they were able to see above and create inclusive institutions that offered ways for them to become Romans. It welcomed diversity (for the time) much more and benefited from it. Benefited from auxiliary forces providing Cavalry support, archers... Benefited from getting ideas from other societies and improving upon them (the Gladius, the Spatha, the Trireme...). Rome never shied away from recognizing better ways of doing things in their enemies and just taking them. Even for gods, they recognized foreign gods are gods that deserve worship just as much and assumed that, often, they were the same gods perceived differently (in this, the greeks did that too to be fair)
In general, the more you learn about greek polis and other ancient societies the more contrast you see with Rome and the more you see that what made Rome great was NOT the warrior-culture, nearly-fascist attributes we see often represented in Media, but rather the opposite. The ability to learn, incorporate different cultures into their empire and the presence of powerful, inclusive institutions that allowed foreigners to become fully Roman..