Rome vs Han essay- want get some opinions

[Anthrophobia]

So why did Rome keep coming back dispite huge defeats all through her history? There is no way that a nomadic culture could survive even a single one of the larger defeats the Romans suffered. As already stated, rival clans would swallow them up.

Coming back from huge defeats isn't something that's just special to Rome. Any successful country came back from huge defeats. The XiongNu of course never suffered "huge" defeats in the first place(because of their manueverability, if anything seems wrong, just RUN AWAY!), that is until the time of WuDi(as a result that WuDi CHEATED by secretely preparing over a GENERATION for war, as well as the luck to have a line of genius generals while the XiongNu had so-so generals). The Han suffered defeats up to 300,000 men and more as well, and Chinese dynasties before them were basically a tug of war, I'm stronger one day, and your stronger the next(right after I suffered a defeat of several hundred thousand men which in short absolutely ruined the economy). It's nothing special. If you can't come back despite a huge defeat, we call that country "exctinct", or that country would lack in power so much that no one would know about it. My theory of the reason why countries can come back from a major defeat is that this country has a stronger economy than its opposing country. Thus it can resupply its manpower, weapons, food supply, and armor faster than the opposing side. Rome against Carthage is a perfect example of this, for it was Rome who had the better economic edge. The Qin vs other Warring States is also a brilliant example, for the Qin's economy is much more geards toward war than the other states(your either a smith, a soldier, or a farmer. Jobs such as acting is out of the question).

Except that the Romans kept a far more open formation than earlier phalanx armies. The whole point of this is to give each soldier more room to manoeuvre (e.g. swing a sword).

That depends on the situation. Even with enough room to swing, a swing needs to have force applied to it, as that is its only advantage over thrusting. Such a short sword is not suited for this occasion(short=less swinging force) against a similar army armed with gladius-like weapons. Can the soldier cut? Of course, if his opponent gives an opening that requires it. But like what I previously stated, a thrust is much more efficient for the gladius rather than a cut, as it is easier to target important organs/weak spots in the armor.
Again, as I said, Polybius lived in the time of the Roman Republic. It is no question that the Roman empire is much more powerful than the Roman Republic, especially after Marius' reforms. Thus, unless you are talking about the Roman Republic, leave poor Polybius alone .