Han had its full time professional soldiers,but the professional army should do some farm work to provide themself ...
Just a note: you're either professional full time, or not. You can be trained, but still not be 'professional', professional here meaning that you're getting paid for your services. You also can't be both full time farmer and soldier.
... and Han Dynasty didn't need to rob other countries to maintain their army.So Rome should expand their land for their soldiers because they had no correct economic policies.
Not sure what you mean by 'correct'. Rome's economic policies might not be correct by today's standards, but back then they were perfect and very successful: wealth all over the empire, peace, social programs, whatever. Their economy was not based on robbing other countries ... if anything, they destroyed too much of what they conquered. Most conquered parts would be better of economically once Roman.
Rome's economy was based on slavery and expansion. The slavery meant cheap labor (and killed off any machine-like inventions). The expansion ensured an ever growing internal market, peace and prosperity, while at the same time allowing for a vast professional army, being active all the time.
Rome back then was a lot like big corporations are nowadays: powerful and growing, with an aggressive M&A department, no real innovative ability, but a good thing to be part of as long as you're not at center stage, at the bottom of the pile, or during a board upheaval. On the other hand, being part of one of its M&A candidates is a lot less fun, especially if you're in any kind of management position.
BJ
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