Here is something that I don't understand. Roman Empire had advanced science, it had lot of people, lot of money and resources, and could have more weapon and soldiers than anyone else. Where did tribes from Asia, who had no advanced technologies, poor economy, no literacy, get the resources and soldiers needed to successfully invade and win against the Empire? Where did they get the weapon? Why they were so numerous if all they did was riding the steppes on their horses? Is riding the steppes on a horse more profitable than building cities, roads, bridges and aqueducts?
Also why don't we see similar things in modern times, why don't wee see poor undeveloped nations successfully invading large developed countries?
The Romans didn't really have that much of a tech advantage vs. steppe riders like the Huns when it came to practical combat. They also had good horsemanship (learning to ride as toddlers) and the valuable ability to fire arrows from horseback.
However, the Huns were kind of an abberation. Most of the migrations/invasions were Germanic forest dwellers. In addition, for the most part it didn't look like an invasion. Many of the tribes were allowed to settle in the empire in exchange for military service, and Germans gradually started occupying the upper echelons of the military caste. By this time, the Western Roman Empire's institutions were just kind of falling apart. The local elites had little incentive to do much about it, and were happy enough to work with the Germans once Odoacer ripped off the bandaid and deposed the last emperor. Italy was actually quite prosperous for the century after the fall, until the Eastern Roman Empire initiated its reconquest and set off a series of wars.
Today's countries are incomparably more centralized than in the times of Rome.
When Georgia fired some missile on Russia (after weeks of harassment by Russian troops at the border), Putin knew about it within seconds. The same thing would have taken days if not weeks in Roman times.
And then, marching an army from a neighboring province again would have taken weeks, or even months if you needed to bring them from farther away. Today, your air force can arrive at any point on your (main) territory in a matter of hours, even for a country the size of Russia, and boots on the ground might take a day or two.
Also, everything about how war is fought and the impact of weapons has changed dramatically. The difference between the destructive power of the greatest (even non-nuclear) weapons that we have versus more common rifles or rockets is colossal. In Roman times, the difference between the best weapon and an improvised club was tiny by comparison.
> Also why don't we see similar things in modern times, why don't wee see poor undeveloped nations successfully invading large developed countries?
We will, in time. But there’s a huge technology gap in weapons and warfare compared to the past. I believe they could conquer and grow by recruiting the people and resources of the conquered. Making larger targets more achievable. So it was a process. It’s not that a conqueror had the resources and people needed to begin with or got them through peaceful growth.
That said, in modern times, the west is so outnumbered and richer than the east that it’s likely only a matter of time before this happens.
Also why don't we see similar things in modern times, why don't wee see poor undeveloped nations successfully invading large developed countries?