Mountians were important to early greek city states because they

From early times the Greeks lived in independent communities isolated from one another by the landscape. Later these communities were organized into poleis or city-states. The mountains prevented large-scale farming and impelled the Greeks to look beyond their borders to new lands where fertile soil was more abundant.

Explanation:

From early times, the Greeks lived in independent communities that were quite isolated from one another due to the landscape/geography. Later on, these communities were organized into polis or city-states. The mountains prevented large-scale farming and impelled the Greeks to look beyond their borders to new lands where there was a greater amount of fertile soil (good soil for planting).

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