Which invaders of the roman empire came from the farthest eastern point

These invasions were by the Goths and the Heruli who lived in Ukraine.

I guess that your referring to to the invaders of the Roman Empire (the Romans came from the same place, Rome). the roman Empire suffered many invasions over several countries before the final invasions.
which led to the fall of the Roman Empire. the westernmost invasions were by Persians. along the eastern borders of the Empire in Asia. The Persians and some fought each other for centuries and conqured each others territories several times.

that should help

high entry costs prevent new producers from entering the market.

explanation:

an oligopoly is a term used to clarify the structure of a particular market, industry, or organization. a market is considered oligopolistic or amazingly focused when it is shared between a few companies.